Ah, co-authored, but that's different thing, isn't it?
Tbh I only know it from squashed PRs.
However:
> "Co-author" is not a git concept. It is a convention in commit messages used by some services, including GitHub. So, the solution is to edit the actual commit message with git commit --amend and add a line to the end:
It's a door opened by git (interpret-trailers), walked through by GitHub with the Co-authored-by key and UI support, GitLab followed.