Drop target for .NET 6 that's no longer supported

[atifaziz]

This PR drops the .NET 6 run-time target that's no longer supported. It reached end-of-life on November 12, 2024.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.28%. Comparing base (0c924d5) to head (e759411).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1104      +/-   ##
==========================================
- Coverage   93.30%   93.28%   -0.02%     
==========================================
  Files         113      113              
  Lines        3448     3439       -9     
  Branches      971      969       -2     
==========================================
- Hits         3217     3208       -9     
  Misses        215      215              
  Partials       16       16              

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