Compile for .NET 6

[natemcmaster]

Helps ensure the tool works when .NET 5 isn't available.

[codecov]

Codecov Report

Merging #103 (65b7b02) into main (ebf2b2d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #103   +/-   ##
=======================================
  Coverage   24.02%   24.02%           
=======================================
  Files          17       17           
  Lines         541      541           
=======================================
  Hits          130      130           
  Misses        411      411           

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