update codecov to v4

[hyrodium]

cf: https://discourse.julialang.org/t/psa-new-version-of-codecov-action-requires-additional-setup/109857

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.72%. Comparing base (5a504b0) to head (b398dcf).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #53       +/-   ##
===========================================
+ Coverage   30.76%   80.72%   +49.95%     
===========================================
  Files           5        5               
  Lines          78       83        +5     
===========================================
+ Hits           24       67       +43     
+ Misses         54       16       -38     

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