[llvm] [workflows] Create a more descriptive title and body when creating a … (PR #80396)

[Fangrui Song via llvm-commits]

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@@ -567,9 +567,15 @@ def create_pull_request(self, owner: str, repo_name: str, branch: str) -> bool:
             print("PR already exists...")
             return True
         try:
+            commit_message = repo.get_commit(commits[-1]).commit.message
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MaskRay wrote:

Let's say we have 3 commits. They can be either of `test-cleanup test-cleanup functional` or `functional test-fixup test-fixup` or `test-cleanup functional test-fixup`.

A heuristic may be to pick the commit with the longest commit message...

https://github.com/llvm/llvm-project/pull/80396