Update setup-dotnet to v4.2.0 and clear old endpoints

[imnasnainaec]

Supersedes #3524

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.55%. Comparing base (0947624) to head (f138905).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3527   +/-   ##
=======================================
  Coverage   74.55%   74.55%           
=======================================
  Files         286      286           
  Lines       11022    11022           
  Branches     1344     1344           
=======================================
  Hits         8217     8217           
  Misses       2418     2418           
  Partials      387      387           

Flag	Coverage Δ
backend	83.62% <ø> (ø)
frontend	66.51% <ø> (ø)

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[hahn-kev]

looks good to me, it does look like ci.dot.net was added but I suspect that would only be used if we were to try and use a nightly build in setup-dotnet so it's probably not worth adding

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @imnasnainaec)