Bump go_router from 14.8.1 to 15.0.0 in /testing_app

Bumps [go_router](https://github.com/flutter/packages/tree/main/packages) from 14.8.1 to 15.0.0.
- [Release notes](https://github.com/flutter/packages/releases)
- [Commits](https://github.com/flutter/packages/commits/go_router-v15.0.0/packages)

---
updated-dependencies:
- dependency-name: go_router
  dependency-version: 15.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

testing_app/pubspec.yaml

@@ -12,7 +12,7 @@ dependencies:
 
   cupertino_icons: ^1.0.3
   provider: ^6.0.2
-  go_router: ">=10.0.0 <15.0.0"
+  go_router: ">=10.0.0 <16.0.0"
 
 dev_dependencies:
   analysis_defaults: