chore(deps): bump the built_value group

Bumps the built_value group in /packages/smithy/smithy with 2 updates: [built_value](https://github.com/google/built_value.dart) and [built_value_generator](https://github.com/google/built_value.dart).


Updates `built_value` 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)

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

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

packages/smithy/smithy/pubspec.yaml

@@ -30,7 +30,7 @@ dependencies:
 dev_dependencies:
   amplify_lints: ">=3.1.0 <3.2.0"
   build_runner: ^2.4.9
-  built_value_generator: 8.8.1
+  built_value_generator: 8.9.2
   json_serializable: 6.8.0
   stack_trace: ^1.10.0
   test: ^1.22.1