[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)

[Anton Korobeynikov via llvm-commits]

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@@ -0,0 +1,36 @@
+name: "Check for private emails used in PRs"
+on: pull_request_target
+permissions:
+  pull-requests: write
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asl wrote:

Sure, can do that

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