Updating the xunit version to one that does not depend on internalabstractions.

test/dotnet-test.Tests/GivenThatWeWantToUseDotnetTestE2EInDesignTimeForMultipleTFms.cs

@@ -6,6 +6,7 @@ using System.Linq;
 using System.Runtime.CompilerServices;
 using FluentAssertions;
 using Microsoft.DotNet.InternalAbstractions;
+using Microsoft.DotNet.PlatformAbstractions;
 using Microsoft.DotNet.ProjectModel;
 using Microsoft.DotNet.TestFramework;
 using Microsoft.DotNet.Tools.Test.Utilities;