Re-enable dotnet/format in build

dotnet/format was [disabled](https://github.com/dotnet/installer/pull/16033) from source-build to unblock the sdk->installer dependency flow.  dotnet/format needed to be upgraded to [net8.0](https://github.com/dotnet/format/pull/1812) first.  Once these changes flow into installer, the repo should be re-enabled.