Bump .NET SDK to 10.0.200 when available

.NET SDK 10.0.200 has been announced but binaries aren't available for download yet.

Once it's published, update `dotnet-version` in all CI workflows:
- `.github/workflows/pull-request.yml`
- `.github/workflows/publish.yml`
- `.github/workflows/preview.yml`

Currently pinned to `10.0.104` as a workaround (the `10.0.1xx` channel band started resolving to `10.0.105` which also isn't available yet).