[llvm] [Github] Fix revisions in code format action reproducers (PR #155193)

[Baranov Victor via llvm-commits]

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@@ -175,9 +181,32 @@ class ClangFormatHelper(FormatHelper):
     name = "clang-format"
     friendly_name = "C/C++ code formatter"
 
+    def _construct_command(self, diff_expression: list[str] | None):
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vbvictor wrote:

It feels strange that `diff_expression` can be `None`.
In `main`, both `start_rev` and `end_rev` are required params so we should always expect `diff_expression` to be non-null.

IMO the main purpose of format-helper is to check formatting from `start_rev` to `end_rev` so if `diff_expression` is none we failed the whole job.

https://github.com/llvm/llvm-project/pull/155193