Add await ref.watch(sharedPreferencesProvider.future) to prevent AsyncValue error during app startup

Author: bizz84

lib/src/routing/app_startup.dart

@@ -3,6 +3,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 import 'package:starter_architecture_flutter_firebase/src/constants/app_sizes.dart';
 import 'package:starter_architecture_flutter_firebase/src/features/onboarding/data/onboarding_repository.dart';
+import 'package:starter_architecture_flutter_firebase/src/utils/shared_preferences_provider.dart';
 
 part 'app_startup.g.dart';
 
@@ -11,12 +12,14 @@ part 'app_startup.g.dart';
 Future<void> appStartup(Ref ref) async {
   ref.onDispose(() {
     // ensure dependent providers are disposed as well
+    ref.invalidate(sharedPreferencesProvider);
     ref.invalidate(onboardingRepositoryProvider);
   });
   // Uncomment this to test that URL-based navigation and deep linking works
   // even when there's a delay in the app startup logic
   // await Future.delayed(Duration(seconds: 1));
   // await for all initialization code to be complete before returning
+  await ref.watch(sharedPreferencesProvider.future);
   await ref.watch(onboardingRepositoryProvider.future);
 }