[main] SDK diff pipeline cannot find msft artifacts

[ellahathaway]

BlobArtifacts is no longer being published by the unified-build pipeline. This breaks the SDK diff tests because the tests look for linux and linux musl msft artifacts in BlobArtifacts.

The msft artifacts can now be found in the <buildname>_Artifacts container. More specifically, we can also find the artifact path and names in the AssetManifests/MergedManifest.xml artifact:

<Blob Id="Sdk/<version>/dotnet-sdk-<version>-linux-x64.tar.gz" DotNetReleaseShipping="true" PipelineArtifactName="AzureLinux_x64_Cross_x64_Artifacts" PipelineArtifactPath="assets/Release/Sdk/<version>/dotnet-sdk-<version>-linux-x64.tar.gz" RepoOrigin="sdk" Visibility="External"/>

This is a regression from dotnet/dotnet#935.