Revert __eq__ removal (#8487)

Refs #8483

stdlib/argparse.pyi

@@ -330,6 +330,7 @@ class Namespace(_AttributeHolder):
     def __getattr__(self, name: str) -> Any: ...
     def __setattr__(self, __name: str, __value: Any) -> None: ...
     def __contains__(self, key: str) -> bool: ...
+    def __eq__(self, other: object) -> bool: ...
 
 class FileType:
     # undocumented