Runtime build is not using source-built packages

[crummel]

In the source-built 6.0 runtime CI build https://dev.azure.com/dnceng/public/_build/results?buildId=1657699&view=logs&j=000ba8e3-34f8-51d2-8d06-9b61f10256d0&t=ca9b6e26-8c16-57f9-673e-2bc0dc655f25&l=11937, the source-built version of Arcade and other packages are not being used. This is specific to the repo source-build legs, not the tarball build. This was discovered because the source-built Arcade should include net6.0 assemblies but the binlog shows it only has net3.1 assemblies. This is not unique to SDK packages; other packages built in Arcade are also missing net6.0 assemblies.

Binlog: runtime-sourcebuild.zip

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[crummel]

This appears to not be unique to runtime; roslyn and sdk source-build legs are also not using the source-built Arcade. Eric St John has a fix for the immediate problem in merged in dotnet/arcade#8597 so we will plan to triage this normally.