chore(deps): bump json_serializable

Bumps the json_serializable group with 1 update in the /packages/aws_signature_v4 directory: [json_serializable](https://github.com/google/json_serializable.dart).


Updates `json_serializable` from 6.8.0 to 6.9.3
- [Release notes](https://github.com/google/json_serializable.dart/releases)
- [Commits](google/json_serializable.dart@json_serializable-v6.8.0...json_serializable-v6.9.3)

---
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>

Author: dependabot[bot]

packages/aws_signature_v4/pubspec.yaml

@@ -26,7 +26,7 @@ dev_dependencies:
   build_verify: ^3.0.0
   build_version: ^2.1.1
   build_web_compilers: ^4.0.0
-  json_serializable: 6.8.0
+  json_serializable: 6.9.3
   stream_channel: ^2.1.0
   test: ^1.22.1