Pin as many deps as possible in 3.9 GPU CI environment

[charlesbluca]

This should make this environment consistent with that used in GPU CI as of https://github.com/rapidsai/dask-build-environment/pull/83

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (3ffba21) 85.56% compared to head (b164005) 85.45%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1292      +/-   ##
==========================================
- Coverage   85.56%   85.45%   -0.12%     
==========================================
  Files          77       77              
  Lines        4255     4255              
  Branches      794      794              
==========================================
- Hits         3641     3636       -5     
- Misses        445      450       +5     
  Partials      169      169              

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