Rename tox virtualenv dir from .env_pudl to .env_tox

[zaneselvans]

No description provided.

[codecov]

Codecov Report

Merging #1586 (f1586eb) into dev (bb573b3) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##             dev   #1586   +/-   ##
=====================================
  Coverage   84.1%   84.1%           
=====================================
  Files         65      65           
  Lines       7224    7224           
=====================================
  Hits        6079    6079           
  Misses      1145    1145           

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