[llvm] [CI] Make email check workflow fail when author's email is private in Github UI (PR #148694)

[via llvm-commits]

github-actions[bot] wrote:

⚠️ We detected that you are using a GitHub private e-mail address to contribute to the repo.<br/> Please turn off [Keep my email addresses private](https://github.com/settings/emails) setting in your account.<br/> See [LLVM Developer Policy](https://llvm.org/docs/DeveloperPolicy.html#email-addresses) and [LLVM Discourse](https://discourse.llvm.org/t/hidden-emails-on-github-should-we-do-something-about-it) for more information.

https://github.com/llvm/llvm-project/pull/148694