Fix test for new group keys behavior for Pandas 2

[caneff]

In Pandas 2, groupby().apply() will append group keys to an index that already has them in cases where the apply is really a transform (the resulting index is same as the incoming one). This is a change from Pandas 1.5.

When running the original test with Pandas 1.5, we get the following warning:

To preserve the previous behavior, use

	>>> .groupby(..., group_keys=False)

To adopt the future behavior and silence this warning, use 

	>>> .groupby(..., group_keys=True)
  df.groupby(['provider']).apply(lambda x: x)

So I set group_keys to False to retain the 1.5 behavior.

[caneff]

R: @tvalentyn

[github-actions]

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[codecov]

Codecov Report

Merging #28566 (99f375f) into master (a722740) will increase coverage by 0.00%.
Report is 44 commits behind head on master.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #28566   +/-   ##
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  Coverage   72.23%   72.23%           
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  Files         684      684           
  Lines      100883   100977   +94     
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+ Hits        72869    72945   +76     
- Misses      26435    26453   +18     
  Partials     1579     1579           

Flag	Coverage Δ
python	82.82% <ø> (-0.01%)	⬇️

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