Update UDS WindowsAuth test to run on Windows only. (dotnet#5397)

src/System.Private.ServiceModel/tests/Scenarios/Binding/UDS/UDSBindingTests.cs

@@ -60,7 +60,7 @@ public static void SecurityModeNone_Echo_RoundTrips_String()
     [WcfFact]
     [OuterLoop]
     [Condition(nameof(Windows_Authentication_Available),
-              nameof(WindowsOrSelfHosted))]
+              nameof(Is_Windows))]
     public void WindowsAuth()
     {
         string testString = new string('a', 3000);