Fix hang in host tests due to test parallelization

This change disables test parallelization in the
PowerShellEditorServices.Test.Host project to avoid a test hang caused by
two test simultaneously choosing the same "random" port numbers for their
tests.  We currently can't detect the same port numbers because the TCP
ports are configured to allow reuse.  Thus, we disable test
parallelization in this assembly so that the tests all run serially,
avoiding the port reuse issue.

Author: daviwil

test/PowerShellEditorServices.Test.Host/AssemblyInfo.cs

@@ -0,0 +1,9 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Xunit;
+
+// Disable test parallelization to avoid port reuse issues
+[assembly: CollectionBehavior(DisableTestParallelization = true)]