[llvm] [GitHub] Add workflow to check author's commit access on new PRs (PR #123593)

[David Spickett via llvm-commits]

DavidSpickett wrote:

I checked, and the labeller action we use for general labels cannot do this sort of check. Just file paths and branch names - https://github.com/actions/labeler?tab=readme-ov-file#match-object.

https://github.com/llvm/llvm-project/pull/123593