Follow up work for `upgrade tooling to 9.0x`

[radical]

#5483

• Diff package build output to ensure contents of packages are unaffected (added by @joperezr)
• Bump sdk version in global.json to rc1 This will come from arcade automatically.
• Tie the sdk for testing version to a dependency from dotnet/sdk like Microsoft.NetCore.App.Ref

cc @joperezr

[radical]

Closing this as a stale issue.