fix pandas v2.1 NumpyEADtype issue

[topper-123]

• Closes pint_pandas won't import using pandas 2.1-dev version  #194
• Executed pre-commit run --all-files with no errors
• The change is fully covered by automated unit tests
• Documented in docs/ as appropriate
• Added an entry to the CHANGES file

Precursor to working on #174.

[topper-123]

A few minor issues that make the test suite fail. These fixes are all backwards compat.

There is still some failures in the test suite when running against v2.1.dev, but fixing those will take some care to ensure the test suite will run in both v2.1 and in older pandas versions, so I'll take those in a separate PR.

[andrewgsavage]

edit: asked in issue instead

[andrewgsavage]

bors r+

[bors]

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• ci
• lint