Disable NSwag as this seems to cause flakiness in dotnet tests.

[kwokkan]

See:

• Tests hang from dotnet test microsoft/vstest#2080
• dotnet test keeps hanging dotnet/aspnetcore#3443
• Dotnet test hangs when running on a multi-project solution microsoft/vstest#2025
• dotnet test hangs when running integration tests with UseWebpackDevMiddleware in Azure DevOps dotnet/aspnetcore#10497
• https://discuss.circleci.com/t/dotnet-core-testing-randomly-times-out/30492/18

[codecov]

Codecov Report

Merging #458 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #458   +/-   ##
=======================================
  Coverage   33.53%   33.53%           
=======================================
  Files         216      216           
  Lines        4082     4082           
  Branches      419      419           
=======================================
  Hits         1369     1369           
  Misses       2713     2713

Flag	Coverage Δ
#dotnet	38.76% <ø> (ø)	⬆️
#npm	10.08% <ø> (ø)	⬆️

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