[llvm] Reapply [workflows] Split pr-code-format into two parts to make it more secure (#78215) (PR #80495)

[James Y Knight via llvm-commits]

https://github.com/jyknight approved this pull request.

Yes, I think it's fine to commit this as-is and do further cleanup in follow-on PRs.

https://github.com/llvm/llvm-project/pull/80495