Support Pandas 2.0

[huard]

Pandas 2.0 released April 3, 2023 breaks test_compare_weights_from_poly_and_grid in test_frontend.py because get_loc no longer supports the method argument.

Removed the method and tolerance arguments in Index.get_loc(). Use index.get_indexer([label], method=..., tolerance=...) instead (GH42269)

https://pandas.pydata.org/docs/dev/whatsnew/v2.0.0.html#removal-of-prior-version-deprecations-changes