Bump google_mobile_ads from 2.4.0 to 3.0.0 in /game_template

Bumps [google_mobile_ads](https://github.com/googleads/googleads-mobile-flutter/tree/main/packages) from 2.4.0 to 3.0.0.
- [Release notes](https://github.com/googleads/googleads-mobile-flutter/releases)
- [Commits](https://github.com/googleads/googleads-mobile-flutter/commits/HEAD/packages)

---
updated-dependencies:
- dependency-name: google_mobile_ads
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

game_template/pubspec.yaml

@@ -26,7 +26,7 @@ dependencies:
   firebase_core: ^2.1.1  # Needed for Crashlytics below
   firebase_crashlytics: ^3.0.3  # Error reporting
   games_services: ^3.0.0  # Achievements and leaderboards
-  google_mobile_ads: ^2.0.1  # Ads
+  google_mobile_ads: ^3.0.0  # Ads
   in_app_purchase: ^3.0.1  # In-app purchases
 
 dev_dependencies: