chore(deps): bump json_serializable

Bumps the json_serializable group in /packages/smithy/smithy with 1 update: [json_serializable](https://github.com/google/json_serializable.dart).


Updates `json_serializable` from 6.8.0 to 6.9.0
- [Release notes](https://github.com/google/json_serializable.dart/releases)
- [Commits](google/json_serializable.dart@json_serializable-v6.8.0...json_serializable-v6.9.0)

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

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

packages/smithy/smithy/pubspec.yaml

@@ -31,6 +31,6 @@ dev_dependencies:
   amplify_lints: ">=3.1.0 <3.2.0"
   build_runner: ^2.4.9
   built_value_generator: 8.8.1
-  json_serializable: 6.8.0
+  json_serializable: 6.9.0
   stack_trace: ^1.10.0
   test: ^1.22.1