Update test_numpy.py

Getting this error for Python 3.9 but not Python 3.10 or 3.11:

```
pandas/tests/extension/test_numpy.py:282: in TestArithmetics
    ) -> type[Exception] | None:
E   TypeError: unsupported operand type(s) for |: 'types.GenericAlias' and 'NoneType'
```

Perhaps what's missing is this import statement?

Signed-off-by: Michael Tiemann <[email protected]>

Author: MichaelTiemannOSC

pandas/tests/extension/test_numpy.py

@@ -15,6 +15,8 @@
 Note: we do not bother with base.BaseIndexTests because NumpyExtensionArray
 will never be held in an Index.
 """
+from __future__ import annotations
+
 import numpy as np
 import pytest