Use local copy of regression data for regression tests

[timothy-nunn]

Moves from getting regression reference data using requests to using the local git client to get the regression references.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.51%. Comparing base (0f65c5e) to head (87eb590).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4122      +/-   ##
==========================================
+ Coverage   47.30%   47.51%   +0.21%     
==========================================
  Files         140      141       +1     
  Lines       29448    29487      +39     
==========================================
+ Hits        13929    14010      +81     
+ Misses      15519    15477      -42     

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