Tell supervisor I am unhappy with grading even though grades won't change I have been working in a group project of six people at university.
I think I made an substantial effort, and would consider me among the two best performers in the group (please accept this as a fact for answering the question). I do not bear grudges against my group, I think we worked well together and I liked working with all of them. I just put more effort in the project, and I am proud of my contribution.

Now the grades have been published, and I have been graded worse than two other students, because of things which were not communicated to be part of the grading process:
We finished the project mid of July. Recently, there has been a presentation of parts of our results, which required some extra work. I am currently abroad in an internship. The two students did some additional experiments for the presentation. I was not aware of these additional experiments, because there was no communication about that on our mailing list, basically the two students just happened to be around. I communicated my internship early, and this was accepted by the supervisor. I think the additional experiments do not outweigh my previous contributions by far. Also, I would have helped with the experiments from abroad (which would have been easily possible, because it's computer science), if I would have known.

I am unhappy with this distinction, because I think it is not fair and does not represent my performance, which is also admitted by the two students with the better grades. For me, it would have been ok, if we all got the same grade.

However, the grades are already published, and there is no good way of changing the grades now (pushing the entire team to the better grade is not an option because of politics; I do not want the two to get a worse grade; I would feel unhappy with only me being upgraded). I know this and I accept this.

Now, should I tell my supervisor, that I am unhappy with the grading and explain my reasons why, even though I know it will change nothing in the grades? I do not want to make accusations or anything, just express my problems with the grading.

I do not want to burn any bridges, and might want to work with this supervisor again in the future.
I would see this as
(i) feedback for my supervisor for the grading process
(ii) a way for me to finish the project and get over the frustration (again, I do not intend to make accusations, just lay out why I am unhappy).

Should I do this or should I just swallow my pride and deal with it?
Unless this decision is somehow going to jeopardize your whole future and not just this one grade then I would suggest to "swallow your pride." You mentioned that you are interested in working with this supervisor in the future. That would certainly be great networking which could bring you a number of opportunities and I wouldn't say risking all of that is worth contesting this one grade (which you may still not be in the right). Leave your pride at the door and reach for your goals only until sometime truly disrespects you. Otherwise try to focus on the positives.