Prevent NuGet audit warnings from failing the CI builds (Lombiq Technologies: OCORE-184)

[Piedone]

NuGet security audit warnings should still show up in VS, and also in CI builds, but as warnings.

Formerly, due to CI builds treating warnings as errors (to prevent introducing new build warnings) these also failed CI builds. This is a problem because security issues being discovered in NuGet packages we use can happen any time, and thus all our CI builds could break anytime, without us changing the code

These warnings should still be addressed ASAP, of course, but they shouldn't block all other development. After #16284 this will happen automatically.

I tried to do this in a way that we still see the warning even in CI builds but couldn't succeed.

FYI what does NOT prevent these warnings from being treated as errors:

• <WarningsNotAsErrors>NU1901;NU1902;NU1903;NU1904</WarningsNotAsErrors> in any or all of the files below (though it should work from a Directory.Build.props, see Solution level NuGetAuditLevel settings NuGet/Home#13022).
  
  I also tried changing these two to include $(WarningsNotAsErrors); but that didn't help:
  
  This only works when set in a csproj file, the one of the project that has an offending dependency. This obviously doesn't scale.
• Adding the following switches to dotnet build: /p:WarningsNotAsErrors=NU1902, -warnNotAsError:NU1902, /warnaserror-:NU1902 or -warnaserror-:NU1902 (old switch, is not accepted at all), -warnAsMessage:NU1902, /property:WarningsNotAsErrors=NU1902.

[hishamco]

Suggested change

	# We disable NuGet audit warnings, see https://learn.microsoft.com/en-us/nuget/reference/errors-and-warnings/nu1901-nu1904.
	# Security issues being discovered in NuGet packages we use can happen any time, and thus all our CI builds that
	# treat warnings as errors could break anytime, without us changing the code. This prevents that. Treaing them as
	# warnings and other better approaches don't work, see https://github.com/OrchardCMS/OrchardCore/pull/16317.
	# We disable NuGet audit warnings, see https://learn.microsoft.com/en-us/nuget/reference/errors-and-warnings/nu1901-nu1904.
	# Security issues being discovered in NuGet packages we use can happen at any time, and thus all our CI builds that
	# treat warnings as errors that could break anytime, without us changing the code. This prevents that. Treating them as
	# warnings and other better approaches don't work, see https://github.com/OrchardCMS/OrchardCore/pull/16317.