Should just be an instant perma-ban (along with closure, obviously).
This is the internet. Real offenders will just submit the next PR with a new alt account.
Than it escalates to a platform issue so you just report them in that case. GitHub enforcement staff handles it
“- Creating alternative accounts specifically to evade moderation action taken by GitHub staff or users”
https://docs.github.com/en/site-policy/acceptable-use-polici...