[llvm] [utils] add `stop_at_sha` to revert_checker's API (PR #152011)

[George Burgess IV via llvm-commits]

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@@ -130,6 +130,20 @@ def test_known_reverts_across_arbitrary_llvm_rev(self) -> None:
             ],
         )
 
+    def test_stop_at_sha_works(self) -> None:
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gburgessiv wrote:

Done

https://github.com/llvm/llvm-project/pull/152011