This does not seem to be a problem with the git clients but with rather
with GitHub. When squashing PRs, GitHub seems to use the username as the
author (if no real name is given?).
For example, the PR I just squashed and merged created a commit by the
author "tobous" (my GitHub user name). But on my local branch, the
author is set correctly.
The problem is probably that I did not have my real name set up in my
GitHub profile. I will have to try it out now that my name is set.
Best regards,
Tobias