Fix pandas BaseIndexer import

[charlesbluca]

In pandas 1.4.0, the BaseIndexer was relocated from pandas.core.window.indexers to pandas.core.indexers.objects, breaking CI as seen in https://github.com/dask-contrib/dask-sql/actions/runs/1737510437.

This PR fixes this import to use pandas.api.indexers, which should work for pandas versions both before and after this relocation.

[codecov-commenter]

Codecov Report

Merging #377 (d2f1e2b) into main (ec97bee) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #377      +/-   ##
==========================================
+ Coverage   95.58%   95.60%   +0.01%     
==========================================
  Files          67       67              
  Lines        2923     2932       +9     
  Branches      546      546              
==========================================
+ Hits         2794     2803       +9     
  Misses         79       79              
  Partials       50       50              

Impacted Files	Coverage Δ
dask_sql/physical/rel/logical/window.py	98.83% <100.00%> (ø)
dask_sql/utils.py	100.00% <0.00%> (ø)
dask_sql/context.py	100.00% <0.00%> (ø)
dask_sql/physical/rex/core/call.py	99.12% <0.00%> (+<0.01%)	⬆️
dask_sql/server/responses.py	97.87% <0.00%> (+0.09%)	⬆️

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