[CI] Fix code formatting workflow (#14999)

The code formatting workflow broke just before pulldown from LLVM trunk.
This PR cherry-picks the relevant commits from LLVM trunk to fix the
bug:
llvm/llvm-project@b3c450d
and
llvm/llvm-project@9572388

Example run: #14998
Fixes #14737

---------

Co-authored-by: Aiden Grossman <[email protected]>
Co-authored-by: Louis Dionne <[email protected]>

Author: 3 people

llvm/utils/git/code-format-helper.py

@@ -225,7 +225,7 @@ def format_run(self, changed_files: List[str], args: FormatArgs) -> Optional[str
                 ext.strip(".")
             )  # Exclude periods since git-clang-format takes extensions without them
         cf_cmd.append("--extensions")
-        cf_cmd.append("'{}'".format(",".join(extensions)))
+        cf_cmd.append(",".join(extensions))
 
         cf_cmd.append("--")
         cf_cmd += cpp_files