chore(deps): bump built_value_generator

Bumps the built_value_generator group in /packages/notifications/push/amplify_push_notifications_pinpoint with 1 update: [built_value_generator](https://github.com/google/built_value.dart).


Updates `built_value_generator` from 8.8.1 to 8.9.2
- [Release notes](https://github.com/google/built_value.dart/releases)
- [Changelog](https://github.com/google/built_value.dart/blob/master/CHANGELOG.md)
- [Commits](https://github.com/google/built_value.dart/commits/v8.9.2)

---
updated-dependencies:
- dependency-name: built_value_generator
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: built_value_generator
...

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

packages/notifications/push/amplify_push_notifications_pinpoint/pubspec.yaml

@@ -33,7 +33,7 @@ dev_dependencies:
   aws_common: ">=0.7.1 <0.8.0"
   aws_signature_v4: ">=0.6.1 <0.7.0"
   build_runner: ^2.4.9
-  built_value_generator: 8.8.1
+  built_value_generator: 8.9.2
   flutter_test:
     sdk: flutter
   mocktail: ^1.0.0