chore(very_good_flame_game): update index.html serviceWorkerVersion

[alestiago]

Running the very_good_flame_game template using Flutter 3.22.0, gives:

Warning: In index.html:42: Local variable for "serviceWorkerVersion" is deprecated. Use
"{{flutter_service_worker_version}}" template token instead.

We should modify the index.html to follow the new Flutter web app initialization.

Requirements

• [ ] Update code to remove the "serviceWorkerVersion" warning
• [ ] Update the index.html according to the new guidelines