Make 'RequiresUnreferencedCodeAttribute' internal.

[prochnowc]

Fixes #1462

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.98%. Comparing base (3cb620f) to head (9bd2239).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1463   +/-   ##
========================================
  Coverage    77.98%   77.98%           
========================================
  Files          211      211           
  Lines         5414     5414           
  Branches      1150     1150           
========================================
  Hits          4222     4222           
  Misses         693      693           
  Partials       499      499           

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[tillig]

There is something up with the dotnet-format part of the build. It's a one-line change, I'm just going to force it through; but I need to make the build work before I can publish a release with it. That will not be today. It will probably be after the weekend.

[tillig]

Thanks! I'll see about fixing the build ASAP.