[llvm] Add github workflow that checks if a private email address was used to contribute to the repo and warn in this case (PR #80514)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Yep. The only issue with that is that the comment might get buried (as I've seen happen with the code formatting action), but the job should also fail when it writes a comment to make that visible. I've put it on my backlog to get those two things done, but if someone else gets to it first, that would be good too.

https://github.com/llvm/llvm-project/pull/80514