[`logging`] Fix assertion bug (#6012)

Fix assertion bug

src/diffusers/utils/logging.py

@@ -213,7 +213,7 @@ def remove_handler(handler: logging.Handler) -> None:
 
     _configure_library_root_logger()
 
-    assert handler is not None and handler not in _get_library_root_logger().handlers
+    assert handler is not None and handler in _get_library_root_logger().handlers
     _get_library_root_logger().removeHandler(handler)