Update pint_array.py

Make type hints compatible with python-3.9 (which requires `Union` and does not support the `|` operator to express type disjunction).

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

pint_pandas/pint_array.py

@@ -2,7 +2,7 @@
 import re
 import warnings
 from importlib.metadata import version
-from typing import Any, Callable, Dict, Optional, cast
+from typing import Any, Callable, Dict, Optional, Union, cast
 
 import numpy as np
 import pandas as pd
@@ -622,7 +622,7 @@ def unique(self):
         data = self._data
         return self._from_sequence(unique(data), dtype=self.dtype)
 
-    def __contains__(self, item) -> bool | np.bool_:
+    def __contains__(self, item) -> Union[bool, np.bool_]:
         if not isinstance(item, _Quantity):
             return False
         elif pd.isna(item.magnitude):