BUG: Respect axis when doing DataFrame.expanding

[gfyoung]

Closes #23372.

[pep8speaks]

Hello @gfyoung! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/window.py !

• There are no PEP8 issues in the file pandas/tests/test_window.py !

[codecov]

Codecov Report

Merging #23402 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #23402      +/-   ##
==========================================
- Coverage   92.21%   92.19%   -0.03%     
==========================================
  Files         161      161              
  Lines       51173    51192      +19     
==========================================
+ Hits        47190    47194       +4     
- Misses       3983     3998      +15

Flag	Coverage Δ
#multiple	90.62% <100%> (-0.03%)	⬇️
#single	42.22% <0%> (-0.02%)	⬇️

Impacted Files	Coverage Δ
pandas/core/window.py	96.4% <100%> (ø)	⬆️
pandas/core/arrays/datetimelike.py	94.01% <0%> (-2.11%)	⬇️
pandas/core/indexes/period.py	91.04% <0%> (-1.12%)	⬇️
pandas/core/dtypes/base.py	100% <0%> (ø)	⬆️
pandas/core/dtypes/missing.py	93.1% <0%> (ø)	⬆️
pandas/core/dtypes/inference.py	98.38% <0%> (ø)	⬆️
pandas/core/dtypes/dtypes.py	95.61% <0%> (ø)	⬆️
pandas/core/dtypes/common.py	94.37% <0%> (ø)	⬆️
pandas/core/dtypes/cast.py	88.92% <0%> (ø)	⬆️
pandas/core/dtypes/concat.py	96.34% <0%> (ø)	⬆️

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[gfyoung]

@jreback : Addressed feedback, and all is green. PTAL.

[jreback]

looks good. minor comments.

[gfyoung]

@jreback : All comments addressed, and everything is green. PTAL.

[jreback]

nice! thanks @gfyoung