gh-95971: Turn @writes_bytecode_files to skip when not running (#95972)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Lib/test/test_importlib/util.py

@@ -298,7 +298,7 @@ def writes_bytecode_files(fxn):
     """Decorator to protect sys.dont_write_bytecode from mutation and to skip
     tests that require it to be set to False."""
     if sys.dont_write_bytecode:
-        return lambda *args, **kwargs: None
+        return unittest.skip("relies on writing bytecode")(fxn)
     @functools.wraps(fxn)
     def wrapper(*args, **kwargs):
         original = sys.dont_write_bytecode