Rename pymc3 to pymc in conda test envs

[AlexAndorra]

Somehow, the test environments still had pymc3 in their name, instead of pymc. So here is a quick (arguably extremely complex) PR to fix this

[codecov]

Codecov Report

Merging #5071 (9a21ce6) into main (b54c8af) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #5071      +/-   ##
==========================================
+ Coverage   78.41%   78.43%   +0.01%     
==========================================
  Files         130      130              
  Lines       24461    24461              
==========================================
+ Hits        19182    19185       +3     
+ Misses       5279     5276       -3     

Impacted Files	Coverage Δ
pymc/parallel_sampling.py	87.33% <0.00%> (+1.00%)	⬆️

[AlexAndorra]

I think the readthedocs test failure is unrelated to this PR -- cc @Sayam753 @OriolAbril

[Sayam753]

Yes. It is unrelated.

And we have a open PR to fix RTD builds - #5070