On Github at least the default setting when sending a PR to a repo lets maintainers submit their own commits to your branch, so if I need to do some cleanup I'l

On Github at least the default setting when sending a PR to a repo lets maintainers submit their own commits to your branch, so if I need to do some cleanup I'll often default to that so the user can get credit for both the PR and the commit. If for some reason that isn't possible, it's still relatively easy to fetch the branch locally, add another commit, and then merge that (either manually or through a separate PR), at which point you can also add a comment with a link to the PR the user created if you want to make sure to give them credit as much as possible when closing the PR. If for some reason you absolutely need to have a single commit (e.g. the commit the user submitted would fail some CI check and not be mergeable even with a follow-up commit to fix it), then it's also usually possible to amend their commit with the changes you need locally and then merge that (unless they happend to be GPG signing their commits or something). I consider this a last resort since it feels a bit weird to attribute code to someone without them actually having written it themself, so if I need to do this I'll generally also add another paragraph the commit message explaining what I added myself (there's probably some built-in way with git to add a co-author or something that someone can fill me in on, but I don't know it right now). The other thing I try to make sure to do is thank each contributor explicitly in the release notes when their commits get merged. A simple "Special thanks to @foo for the fix for bug X, @bar for the implementation of feature Y, and @baz for improving the documentation of Z!" is a small amount of effort that I think can go a long way in making contributors feel welcome and appreciated.