Bump google_mobile_ads from 3.1.0 to 4.0.0 (#9)

Bumps [google_mobile_ads](https://github.com/googleads/googleads-mobile-flutter/tree/main/packages) from 3.1.0 to 4.0.0.
- [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
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pubspec.yaml

@@ -29,7 +29,7 @@ dependencies:
   # state management
   provider: ^6.0.5
   # Google Mobile Ads 
-  google_mobile_ads: ^3.0.0 
+  google_mobile_ads: ^4.0.0 
   # share content from  Flutter app
   share_plus: ^7.0.2
   # launch web URLs