refactor: increase background audio volume to 0.2 and update associated assets

lib/features/question/presentation/bloc/question_bloc.dart

@@ -154,7 +154,7 @@ class QuestionBloc extends Bloc<QuestionEvent, QuestionState> {
     if (!_mainAudioService.isMuted) {
       await Future.wait([
         _mainAudioService.setVolume(volume: MyConstants.questionAudioVolume),
-        _backgroundAudioService.setVolume(volume: 0.1),
+        _backgroundAudioService.setVolume(volume: 0.2),
       ]);
     }
     await _backgroundAudioService.play();
@@ -181,7 +181,7 @@ class QuestionBloc extends Bloc<QuestionEvent, QuestionState> {
   Future<void> changeMute() async {
     await Future.wait([
       _mainAudioService.changeMute(newVolume: MyConstants.questionAudioVolume),
-      _backgroundAudioService.changeMute(newVolume: 0.1),
+      _backgroundAudioService.changeMute(newVolume: 0.2),
       _effectAudioService.changeMute(),
     ]);
   }