I'm going to self-host my git repos. Any recommendations?

The git+nginx would suffice but it does not offer GUI. I need one to see the changes proposed (aka PRs).

Gitea is nice, but a bit overkill for my needs. I don't need CI, files hosting, issues, team members, releases, wiki, forking/watching/staring, etc.

Gitea is pretty light on resources so even though it has a extra functionality you don't need it's not really a resource pig. Unlike say, GitLab.

Gitea requires a database which is unwanted feature for "git server" in my little world.

I'm just looking for "website" (read: interface) that list files over HTTPS, with the ability to show nice looking diffs. Some sort of ssh keys(?) to prevent unauthorized access etc.

https://github.com/sitaramc/gitolite

I've not used it personally though, so no idea how well it works in practise.