revert codecov action upgrade

[maskarb]

See codecov/feedback#264

This PR reverts the codecov v4 upgrade because dependabot PRs cannot upload coverage reports.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (00e6621) 86.07% compared to head (c68385f) 85.12%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #294      +/-   ##
==========================================
- Coverage   86.07%   85.12%   -0.95%     
==========================================
  Files          13       13              
  Lines        2162     2730     +568     
==========================================
+ Hits         1861     2324     +463     
- Misses        220      325     +105     
  Partials       81       81              

Flag	Coverage Δ
unittests	85.12% <ø> (-0.95%)	⬇️

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see 13 files with indirect coverage changes

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