They can clone the repo, make changes, and then push. On the server, you can have a hook that checks if the commit only contains appropriate issue changes, and apply just those.
Sure, a little more complicated than “Create Issue”, but not that much for devs. We could even simplify the workflow with e.g. git-issue or something like that, similar to e.g. git-send-email.
git issue init “There is a problem”
git issue push
git issue get 6 # short for issue@{6}