Replace the unused local variable output with _

Author: shenxianpeng

tests/test_clang_format.py

@@ -49,5 +49,5 @@ def test_run_clang_format_invalid(args, expected_retval, tmp_path):
 def test_run_clang_format_dry_run(args, expected_retval, tmp_path):
     # copy test file to tmp_path to prevent modifying repo data
     test_file = tmp_path / "main.c"
-    ret, output = run_clang_format(['--dry-run', str(test_file)])
+    ret, _ = run_clang_format(['--dry-run', str(test_file)])
     assert ret == -1  # Dry run should not fail