I have already decided I'm leaving the company since I really don't
find any reason to try to make him learn how to value others. He is a
senior and if he cannot understand this simple thing by now, I don't
think he will change now.

My question is, should I raise an issue to his boss while I am still
in the company?

No. Take the high road here.

Find your next job, get and accept an offer, give your notice and work the notice period, then put this job behind you.

Trying to raise this issue with his boss will just make you look petty, and won't do anything positive for you. It certainly won't endear you to your boss or anyone else in the company.

It's understandable that you are angry. But knowing that you will be gone soon should make it tolerable.

Though the common consensus is "no, might look bad on you" in other answers already given, I disagree. I think you should voice the reason why you're leaving. No need to shout it from the roof-tops, but your boss (senior developers' superior at least) has to know. Why?

I had a PR with a month's work. He squash-merged the PR in his own pc, so all the code became his property

This (apart from the "software-industry" tag) told me you're in the coding side of software.

Unhappiness among your developers (as a boss) is horrifying, especially if you don't know why. As such, when one leaves, it would be in the bosses (very great and) best interest to find out why to prevent someone else leaving for the same reason (which sometimes means that the senior needs to take a hike). This would be true for any type of department, but more so for coders, as they're in extremely short supply.

You didn't tag a location, so, unless your culture is to keep such information to yourself, your boss should know.

(Unless, of course, the boss is the same kind of person as that senior developer, then, alas, just take it on the chin.)

Aside from correcting him in front of others to claim credit for it, there really is not a lot that you can do.

You said you're leaving the company? In time it will become evident to others when "his" productivity goes down. Personally, I would not go out of my way to make waves, but quietly move on.

tl;dr: It's heavily culture dependent, but not mentioning it is a selfish decision. That does not make it the wrong decision, but be aware that it's definitely the selfish decision. Bringing it up as a "this is what I felt and for this reason I felt like we didn't function well as a team"-type of statement seems fairly safe and worth the minimal risk (although risk dependents once again on culture).

^{Note: This answer is written under the assumption that you did at least once express to your team lead in some way that this part of his behavior is demotivating you.}

Culture

The absolute most important thing to realize here is that culture matters here a lot. In the Netherlands (as long as you aren't a foreigner) one would be nearly "expected" to mention something like this, but in countries with a great authoritative distance (it's a term one academic article used to identify the amount of criticism one is expected to give if one thinks their boss(es) are doing something wrong) it becomes less and less acceptable.

So what if it's at least acceptable?

Ignoring the option that it's literally unacceptable to voice an opinion - which as stated is culture dependent - the question becomes whether it's worth mentioning something like this. The way I would look at this is through the identification of all the stakeholders in your decision. The specific stakeholders you care about will depend a lot on culture once again though. American culture will for example be all about you exclusively, east European will care a lot about friends and thus colleagues, etc. etc.

You: Unless you are considering staying there is zero benefit to you mentioning anything. This seems to be what most of the answers are focusing on. If however you are considering staying at all it might be worth mentioning it. I have seen at least one case where an employee mentioned that the reason they wanted to leave was one of their bosses and it turned out others had brought up the same issue so the boss was fired instead and the employee stayed in the company for a long while afterwards.

The danger - as brought up in the other answers - is of course that the boss' boss will dismiss your complaint out of hand and that this might reflect negatively on his opinion of your character. Whether this matters at all is primarily a question of whether your culture typically requires recommendation letters (or similar) from previous employers and whether your culture actually writes those recommendation letters in an honest way (certain parts of the US for example will not risk writing a negative letter out of fear that it might cause legal trouble). The former combination (frank recommendation letters) seems to be pretty rare as far as I know.

Colleagues: The opposite perspective on the "shared complaints"-point is that if you don't at least hint at this issue there will be no past feedback in the future to back up an employee who might complain about the same thing. In other words by bringing it up you may end up helping either current or future colleagues who will have to work with this team lead.

There seems to be no downside to bringing this up for your colleagues.

The boss/company: Despite the fact that the boss might dismiss any feedback out of hand, in my experience it's the bosses that do accept feedback that survive the longest and are the most efficient at their job. Obviously feedback is better than no feedback and for the boss/company there is zero downside to receiving feedback.

Conclusion

If your culture would accept such feedback it's frankly an egoistic decision to not bring it up. Being selfish is however not always the wrong decision (e.g. if I would have to depend on a recommendation letter from the company in the future), but don't deceive yourself that it's the selfish decision. Whether your colleagues are worth the - very possibly non-existent - sacrifice will depend on your relationship with them. Personally I would recommend bringing it up as a minor point in the exit interview at least, without blowing it up. So something like

I also often felt that <team lead> was taking some credit for my work - rather than describing stuff as a team effort - which demotivated me occasionally. I just didn't feel like we functioned well as a team.

My question is, should I raise an issue to his boss while I am still
in the company?

No- that's not your job and could actually backfire on you/make you look bad depending on how the boss interprets the information prior to you leaving.

I would quietly leave and move on to better opportunities. There are always coworkers who we do not like to work with, since you are already taking action by leaving the company, there is nothing else left to do.

Hopefully, you'll find another job you like better, nonetheless it may take a while before you do so, and you might be unlucky to discover that every job available out there has a much lower pay-range than you do. Case in point: Always think what you can or should do if you were stuck at your current job.

The first thing you can and should do is talking directly to him.
Make his and your responsibilities clear between both of you. In the worst case do make clear to him you are worried that you might lose your job for having your reputation smeared.

If he's an arrogant person you cannot talk to in any way, seek HR.
Tell them the situation, explain this is a problem for everyone and not just for you. Ask HR to do some leadership training or whatever. Also ask them to make some campaign so that HR will motivate other people to bring similar complaints. Just keep in mind that HR wants to solve the company's problem not your problem.

If you do talk to his boss...
Try to have a good proposal. Maybe suggested a few things you could explicitly have on your shoulders, such that the guy you are complaining about may no longer be a problem for you. If you negotiate well, you could be on a faster track to a promotion. Know that this is risky, and talk with a lot of caution. Avoid doing this if you are not willing to leave the company.

The whole point of a quiet exit interview is to not burn bridges by being petty, but the bridges are already on fire if no one knows how much you really work.

By keeping quiet the following issues arise:

• Your boss, coworkers, etc won't be able to recommend you because they'll think you did less than you actually did; such a reputation is definitely important.


• Your boss won't be aware of the situation and will be unable to deal with the growing discontent if any other quiet coworkers go through the same issues.


• Tied to the previous one, any coworkers that happen to raise such an issue won't have any precedence to help their case.

A calm objective conversation about the issues you faced; the stolen PR, your discomfort from having the team lead explicitly take all the credit in a public meeting, etc, won't result in bad blood.

But if you're afraid of speaking up, of being unable to stay collected during the conversation or if the culture is pretty extreme about negatively talking about other people you might have no choice but to face the negatives.

As other people mentioned, the first step should be speaking with the lead in question and trying to work things out from there. Things might improve. If they don't and you still wish to quit, then Speaking from (the) experience (of this one person):

Doing so will probably make you look bad. If you weren't a stand-out employee, then it will mostly be an issue of "he said-she said" and you'll lose to your senior. I lost, even with documented events and other evidence.

But it will put the senior on the radar too. And at some point after you're gone, that senior will have to improve, or it will be the end for them too. At that point, you'll be gone, so you won't know the outcome and you certainly won't hear someone say "Oh! OP was right!" It will mostly just be an empty moral stand at the cost of your reputation.

If that's the desired outcome, then go for it.