Avoid async void in SKXamlCanvas. (#2720)

The async void will terminate here. And we can ignore the Dispatcher.RunAsync result and we can receive the exception from TaskScheduler.UnobservedTaskException.

See dotnet/runtime#76367

source/SkiaSharp.Views.Uno/SkiaSharp.Views.Uno.WinUI.Shared/SKXamlCanvas.cs

@@ -125,12 +125,12 @@ private void OnUnloaded(object sender, RoutedEventArgs e)
 			display.DpiChanged -= OnDpiChanged;
 		}
 
-		public new async void Invalidate()
+		public new void Invalidate()
 		{
 			if (Dispatcher.HasThreadAccess)
 				DoInvalidate();
 			else
-				await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, DoInvalidate);
+				_ = Dispatcher.RunAsync(CoreDispatcherPriority.Normal, DoInvalidate);
 		}
 
 		partial void DoLoaded();