TYP: ALL_NUMPY_DTYPES mypy errors with numpy-1.20
prevents mypy errors

pandas/_testing/__init__.py:122: error: Unsupported operand types for + ("List[Union[ExtensionDtype, Union[str, dtype[Any]], Type[str], Type[float], Type[int], Type[complex], Type[bool], Type[object]]]" and "List[object]")  [operator]
pandas/_testing/__init__.py:123: error: Unsupported operand types for + ("List[Union[ExtensionDtype, Union[str, dtype[Any]], Type[str], Type[float], Type[int], Type[complex], Type[bool], Type[object]]]" and "List[object]")  [operator]
pandas/_testing/__init__.py:124: error: Unsupported operand types for + ("List[Union[ExtensionDtype, Union[str, dtype[Any]], Type[str], Type[float], Type[int], Type[complex], Type[bool], Type[object]]]" and "List[object]")  [operator]