[release/10.0.1xx] PoisonTests failing in `CentOSStream10_Offline_PreviousSourceBuiltSdk`

[Winniexu01]

Failing build (Internal Microsoft link)

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[MichaelSimons]

This is a result of dotnet/sdk#50354 where the .NET Standard 2.1 targeting pack was removed from the sdk. The baseline should be updated accordingly.

[MichaelSimons]

[Triage] Closing as fixed with dotnet/dotnet#2178. This will need to be forward ported to main once the SDK change flows.