Fix NuGet badges

[martincostello]

Use shields.io for NuGet badges.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.35%. Comparing base (3d1da2f) to head (31acd1a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2279      +/-   ##
==========================================
+ Coverage   85.33%   85.35%   +0.02%     
==========================================
  Files         313      313              
  Lines        7444     7444              
  Branches     1122     1122              
==========================================
+ Hits         6352     6354       +2     
+ Misses        746      745       -1     
+ Partials      346      345       -1     

Flag	Coverage Δ
linux	85.35% <ø> (+0.02%)	⬆️
macos	85.33% <ø> (ø)
windows	85.33% <ø> (ø)

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