fix: ignore coverage for dead code

lib/game/pinball_game.dart

@@ -192,6 +192,7 @@ class DebugPinballGame extends PinballGame with FPSCounter {
   // TODO(allisonryan0002): Remove after google letters have been correctly
   // placed.
   // ignore: unused_element
+  // coverage:ignore-start
   Future<void> _loadBackground() async {
     final sprite = await loadSprite(
       Assets.images.components.background.path,
@@ -206,6 +207,7 @@ class DebugPinballGame extends PinballGame with FPSCounter {
 
     await add(spriteComponent);
   }
+  // coverage:ignore-end
 
   @override
   void onTapUp(TapUpInfo info) {