Automerge: fix #163478: false positive in the github actions undef warning

Happened with 'undef,' -- comma not being recognized as a word boundary

Author: nunoplopes

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

@@ -391,7 +391,7 @@ def format_run(self, changed_files: List[str], args: FormatArgs) -> Optional[str
             return None
 
         # Use git to find files that have had a change in the number of undefs
-        regex = "([^a-zA-Z0-9#_-]undef[^a-zA-Z0-9_-]|UndefValue::get)"
+        regex = "([^a-zA-Z0-9#_-]undef[^a-zA-Z0-9,_-]|UndefValue::get)"
         cmd = ["git", "diff", "-U0", "--pickaxe-regex", "-S", regex]
 
         if args.start_rev and args.end_rev: