[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]

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

LGTM. Logic looks good, but not exactly sure of all the details on how Github hides emails. Post-commit analysis of the emails in the commit log to make sure this has the intended effect would definitely be good, but was probably planned anyways.

Thanks for working on this issue!

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