refactor: grouped BumperNoiseBehavior (#409)

Co-authored-by: Jochum van der Ploeg <jochum@vdploeg.net>
Co-authored-by: Allison Ryan <77211884+allisonryan0002@users.noreply.github.com>

test/game/behaviors/bumper_noise_behavior_test.dart

@@ -36,8 +36,7 @@ class _MockContact extends Mock implements Contact {}
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
 
-  group('BumperNoiseBehavior', () {});
-
+  group('BumperNoiseBehavior', () {
     late PinballAudioPlayer audioPlayer;
     final flameTester = FlameTester(_TestGame.new);
 
@@ -58,4 +57,5 @@ void main() {
         verify(() => audioPlayer.play(PinballAudio.bumper)).called(1);
       },
     );
+  });
 }