Resolve Traversable.open failure for 3.13 beta 4 (#12412)

Author: max-muoto

stdlib/@tests/stubtest_allowlists/py313.txt

@@ -166,6 +166,7 @@ unittest.TestCase.__init_subclass__
 unittest.case.TestCase.__init_subclass__
 
 # Problematic protocol signature at runtime, see source code comments.
+importlib.abc.Traversable.open
 importlib.resources.abc.Traversable.open
 
 # Deprecation wrapper classes; their methods are just pass-through, so we can ignore them.