Verify if `dotnet test` for MTP should propagate DOTNET_ROOT similar to dotnet run

[Youssef1313]

Only a quick look through dotnet run, I see:

sdk/src/Cli/dotnet/Commands/Run/RunCommand.cs

Lines 352 to 355 in 846dfc6

	var rootVariableName = EnvironmentVariableNames.TryGetDotNetRootVariableName(
	project.GetPropertyValue("RuntimeIdentifier"),
	project.GetPropertyValue("DefaultAppHostRuntimeIdentifier"),
	project.GetPropertyValue("TargetFrameworkVersion"));

I'm not sure if we should use that for the new dotnet test for MTP or not, especially that in .NET 10 there is local SDK support now in global.json:

https://github.com/dotnet/designs/blob/238ca0202ea5df96d378a06c01960fc289aba166/accepted/2025/local-sdk-global-json.md

But at least we should also verify whether or not the local SDK works correctly with the new dotnet test.