[llvm] github-automation.py: Avoid duplicate pings (PR #184321)

[David Spickett via llvm-commits]

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@@ -673,7 +673,8 @@ def pr_request_review(self, pr: github.PullRequest.PullRequest):
                 for review in pull.get_reviews():
                     if review.state != "APPROVED":
                         continue
-                    reviewers.append(review.user.login)
+                    if review.user.login not in reviewers:
----------------
DavidSpickett wrote:

And I thought about using a set here but:
A: it's more cryptic (have to look to previous lines to know it's a set)
B: then we have to think about order or not, not that it really matters here but it's not even worth having to think about

https://github.com/llvm/llvm-project/pull/184321