fix: Avoid instantiating Window for WPF head

src/ToDo.UI/App.xaml.cs

@@ -35,7 +35,7 @@ public sealed partial class App : Application
 		}
 #endif
 
-#if NET5_0_OR_GREATER && WINDOWS
+#if NET5_0_OR_GREATER && WINDOWS && !HAS_UNO
 		_window = new Window();
 #else
 		_window = Microsoft.UI.Xaml.Window.Current;