Fix missing .UseAndroid()

src/Android/Avalonia.Android/AvaloniaMainActivity.App.cs

@@ -11,5 +11,5 @@ namespace Avalonia.Android;
 public class AvaloniaMainActivity<TApp> : AvaloniaMainActivity
     where TApp : Application, new()
 {
-    protected override AppBuilder CreateAppBuilder() => AppBuilder.Configure<TApp>();
+    protected override AppBuilder CreateAppBuilder() => AppBuilder.Configure<TApp>().UseAndroid();
 }