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

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

I think this is the relevant line in the Github documentation:
> For pull requests from a forked repository to the base repository, GitHub sends the pull_request, issue_comment, pull_request_review_comment, pull_request_review, and pull_request_target events to the base repository. No pull request events occur on the forked repository.

So it uses the workflow definition from the base branch, but then tries to use the script from the PR branch, where it doesn't exist in most cases. So pulling the scripts from the main branch should fix the issue.

LGTM, other than a couple minor nits.

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