Enable NuGet Audit in source-build-reference-packages

[ViktorHofer]

See dotnet/arcade#15019 for more details

Also see dotnet/source-build-reference-packages#1016 which attempted turning it on.

[MichaelSimons]

I don't think this makes sense in SBRP for the actual reference packages. We have recently changed our stance on vulnerabilities within the reference packages. See #4838. We are no longer lifting vulnerable versions as there is no vulnerabilities in reference packages. By lifting packages we have created a maintenance burden with no benefit. We are also adding another difference in how SB builds the product vs the Microsoft build. There would be value in enabling nuget audit for the repo's infrastructure like the generate tooling.

[ViktorHofer]

There would be value in enabling nuget audit for the repo's infrastructure like the generate tooling.

That's possible as the configuration of NuGet Audit is driven by msbuild properties.