Code snippets targeting .NET 9 fail to build in the CI

[kouvel]

See #9943. It looks like the CI job is attempting to build the code snippet project with a .NET 8 SDK: https://github.com/dotnet/dotnet-api-docs/actions/runs/9194367833/job/25287610176?pr=9943#step:6:50

Since the code snippet uses a type that was exposed in .NET 9, it can only be built with a .NET 9 SDK.

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.

[kouvel]

Looks to be fixed by #9947. Thanks @gewarren!