Initialize the ALC for the runspace tests

This initialization was moved out of the native host and into the
managed host, so the same setup must now be done before tests.

test/csharp/test_Runspace.cs

@@ -13,6 +13,12 @@ namespace PSTests
         private static int count = 3;
         private static string script = String.Format($"get-process | select-object -first {count}");
 
+        // Initialize the Core PowerShell AssemblyLoadContext
+        public RunspaceTests()
+        {
+            PowerShellAssemblyLoadContextInitializer.SetPowerShellAssemblyLoadContext(AppContext.BaseDirectory);
+        }
+
         [Fact]
         public void TestRunspaceWithPipeline()
         {