fix logic in app initialization

Labs/CanvasLayout/Tests/CanvasLayout.UnitTests.Uwp/UnitTestApp.xaml.cs

@@ -49,7 +49,7 @@ namespace CanvasLayout.UnitTests.Uwp
 
             // Do not repeat app initialization when the Window already has content,
             // just ensure that the window is active
-            if (Window.Current.Content is Frame rootFrame)
+            if (Window.Current.Content is not Frame rootFrame)
             {
                 // Create a Frame to act as the navigation context and navigate to the first page
                 rootFrame = new Frame();

Tests/CommunityToolkit.Labs.UnitTests.Uwp/UnitTestApp.xaml.cs

@@ -49,7 +49,7 @@ namespace CommunityToolkit.Labs.UnitTests.Uwp
 
             // Do not repeat app initialization when the Window already has content,
             // just ensure that the window is active
-            if (Window.Current.Content is Frame rootFrame)
+            if (Window.Current.Content is not Frame rootFrame)
             {
                 // Create a Frame to act as the navigation context and navigate to the first page
                 rootFrame = new Frame();