[clang] Improve clang-format-diff help output (PR #73491)

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github-actions[bot] wrote:

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``````````bash
darker --check --diff -r 772f296214e10323ca16921c02b1852307b7d51b..788d03126f95ffc8d3b9701fdba73bb931e25cfc clang/tools/clang-format/clang-format-diff.py
``````````

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<details>
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View the diff from darker here.
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``````````diff
--- clang-format-diff.py	2023-11-27 09:17:32.000000 +0000
+++ clang-format-diff.py	2023-11-27 09:25:15.926747 +0000
@@ -38,11 +38,11 @@
 
 def main():
     basename = os.path.basename(sys.argv[0])
     parser = argparse.ArgumentParser(
         description=__doc__.format(clang_format_diff=basename),
-        formatter_class=argparse.RawDescriptionHelpFormatter
+        formatter_class=argparse.RawDescriptionHelpFormatter,
     )
     parser.add_argument(
         "-i",
         action="store_true",
         default=False,

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https://github.com/llvm/llvm-project/pull/73491