[release/9.0] Stage 2 prebuilt - Microsoft.NETCore.Platforms.3.1.0

[MichaelSimons]

The following stage 2 prebuilt is being detected. This was discovered after fixing - dotnet/sdk#43436

<Usage Id="Microsoft.NETCore.Platforms" Version="3.1.0" />

This was caught in a Microsoft internal test build

[ellahathaway]

The prebuilt usage report does not indicate which repo this prebuilt is originating from:

<Usage Id="Microsoft.NETCore.Platforms" Version="3.1.0" />