Historically when we've hit releases for a new .NET version we've adopted that version. We should consider doing that for .NET 9 as well.

Items

• Retarget to Arcade 9 and build dor dotnet 9 (Done: Retargeting to .NET 9  #10484)
• Update subscriptions to Microsoft.DotNet.Arcade.Sdk from .NET ENG 8 To ".NET Eng - Latest" : Updated subscription: fc4faec0-9ee6-43b9-bc7a-08da8607f4c7
• Unfreeze the xunit version #10557
• [Kitten] Remove APICompat workaround once 8.0.2 or 9.xxx is consumed #9720
• Change xliff-tasks dependency in Version.Details.xml when consuming Arcade 9 #9366
• Document the process of retargeting #10576