Unfortunately Anubis wouldn't stop the bots, it would just slow them down.

Anubis just adds proof of work, AKA computation, to your requests. It's why your browser takes a second before it can access the site. It's nothing for things on your scale, but it's a fuck ton of time and money for large scraping operations accessing millions of links every day.

For a bot submitting PRs though, it's not gonna be a meaningful hindrance unless the person is specifically running a bot designed to make thousands of PRs every day, which a lot of these aren't.

Really unfortunate.