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 83.82%. Comparing base (9fb2682) to head (7240697).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #747   +/-   ##
=======================================
  Coverage   83.82%   83.82%           
=======================================
  Files          28       28           
  Lines         674      674           
  Branches      151      151           
=======================================
  Hits          565      565           
  Misses         67       67           
  Partials       42       42           

Flag	Coverage Δ
linux	83.23% <ø> (ø)
macos	83.08% <ø> (+0.44%)	⬆️
windows	82.78% <ø> (ø)

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