[llvm] [workflows] Delete user branches that are too long (PR #82845)

[Tobias Hieta via llvm-commits]

tru wrote:

> > > For git push at least, deleting the branch closes the PR.
> > 
> > 
> > Do actions have the ability to make comments on PRs? It would be less user-hostile to have it leave a comment explaining what happened, and why their PR was being closed.
> 
> Yes, we can do that. Can we always guarantee there will be a PR? If not, I was thinking we could create an issue and @mention the user.

no it's not guaranteed, and probably not if you run the workflow on branch create, then most likely the PR hasn't been opened yet. I think some kind of notification for the user would be good. If we file an issue, that can be pretty spammy for the repo, don't you think? maybe we have a single issue that we @ mention people in the comments?

https://github.com/llvm/llvm-project/pull/82845