Arcade 6 never restores required packages for publish

[jmarolf]

• This issue is blocking

I am unable move roslyn to a newer arcade as packages that are imported in the publish task are never restored

##[error].packages/microsoft.dotnet.arcade.sdk/6.0.0-beta.21152.1/tools/Publish.proj(50,3): error MSB4019:
 (NETCORE_ENGINEERING_TELEMETRY=Publish) The imported project "/home/vsts/work/1/s/.packages/microsoft.dotnet.build.tasks.feed/6.0.0-beta.21152.1/build/Microsoft.DotNet.Build.Tasks.Feed.targets" was not found. Confirm that the expression in the Import declaration "/home/vsts/work/1/s/.packages/microsoft.dotnet.build.tasks.feed/6.0.0-beta.21152.1/build/Microsoft.DotNet.Build.Tasks.Feed.targets" is correct, and that the file exists on disk.

[jmarolf]

This is not an arcade issue.