Adds <RollForward>LatestMajor</RollForward> to the test project so the net8.0 testhost can run on hosts that only have a newer .NET runtime installed (e.g. CI hosts with .NET 10 only). Locally with .NET 8 present this is a no-op; on the runner with .NET 10.0.8 the testhost will roll forward instead of aborting with 'You must install or update .NET to run this application'.
GraceSolutions
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