chore: update GitHub sponsors link

- Change the GitHub sponsors link in the pubspec.yaml file
- Updated the link from 'flutter-news-app-full-source-code-toolkit' to 'flutter-news-app-full-source-code'

Author: fulleni

pubspec.yaml

@@ -7,7 +7,7 @@ homepage: https://flutter-news-app-full-source-code.github.io/docs/
 documentation: https://flutter-news-app-full-source-code.github.io/docs/getting-started/
 issue_tracker: https://github.com/flutter-news-app-full-source-code/flutter-news-app-mobile-client-full-source-code/issues
 funding:
-  - https://github.com/sponsors/flutter-news-app-full-source-code-toolkit
+  - https://github.com/sponsors/flutter-news-app-full-source-code
 topics:
   - flutter-news-app
   - flutter-news-app-mobile-client