[Fix] revise pip upgrade for win-ci

[LeoXing1996]

pip install --upgrade pip is failing on windows GitHub actions runners with v22.0.

[codecov]

Codecov Report

Merging #311 (28f60cb) into master (6bce6ed) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #311      +/-   ##
==========================================
- Coverage   74.81%   74.78%   -0.04%     
==========================================
  Files         145      145              
  Lines       10912    10912              
  Branches     2145     2145              
==========================================
- Hits         8164     8160       -4     
- Misses       2212     2214       +2     
- Partials      536      538       +2     

Flag	Coverage Δ
unittests	74.78% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...chitectures/stylegan/generator_discriminator_v1.py	89.83% <0.00%> (-1.13%)	⬇️
...chitectures/stylegan/generator_discriminator_v2.py	88.83% <0.00%> (-0.94%)	⬇️

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