Rework conda config in GHA workflows; relax test baselines

[blnicho]

Fixes # .

Summary/Motivation:

This cleans up and reworks the conda configuration code in our GHA workflows which will hopefully resolve the broken Windows GHA jobs. This PR includes the changes from #3805 and #3809.

Changes proposed in this PR:

• Rework conda config code in GHA workflows

Legal Acknowledgement

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1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.43%. Comparing base (a079b25) to head (3010cf5).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3810      +/-   ##
==========================================
+ Coverage   89.41%   89.43%   +0.01%     
==========================================
  Files         909      909              
  Lines      105579   105579              
==========================================
+ Hits        94407    94422      +15     
+ Misses      11172    11157      -15     

Flag	Coverage Δ
builders	29.11% <ø> (-0.01%)	⬇️
default	86.04% <ø> (?)
expensive	35.76% <ø> (?)
linux	86.74% <ø> (-2.45%)	⬇️
linux_other	86.74% <ø> (+0.01%)	⬆️
osx	82.88% <ø> (ø)
win	84.99% <ø> (+<0.01%)	⬆️
win_other	84.99% <ø> (+<0.01%)	⬆️

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