Disable pipenv verification in CI

[krzentner]

This is a workaround for #2307

[codecov]

Codecov Report

Merging #2308 (93009b3) into master (3a57885) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2308      +/-   ##
==========================================
- Coverage   91.24%   91.21%   -0.04%     
==========================================
  Files         199      199              
  Lines       10981    10981              
  Branches     1389     1389              
==========================================
- Hits        10020    10016       -4     
- Misses        700      701       +1     
- Partials      261      264       +3     

Impacted Files	Coverage Δ
...rage/tf/optimizers/conjugate_gradient_optimizer.py	81.90% <0.00%> (-1.81%)	⬇️

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