Bump json_serializable in /experimental/web_dashboard (#1177)

Bumps [json_serializable](https://github.com/google/json_serializable.dart) from 6.1.6 to 6.2.0.
- [Release notes](https://github.com/google/json_serializable.dart/releases)
- [Commits](https://github.com/google/json_serializable.dart/compare/json_serializable-v6.1.6...json_serializable-v6.2.0)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

experimental/web_dashboard/pubspec.lock

@@ -393,14 +393,14 @@ packages:
       name: json_annotation
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.4.0"
+    version: "4.5.0"
   json_serializable:
     dependency: "direct dev"
     description:
       name: json_serializable
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "6.1.6"
+    version: "6.2.0"
   lints:
     dependency: transitive
     description:

experimental/web_dashboard/pubspec.yaml

@@ -20,7 +20,7 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
   build_runner: ^2.1.0
-  json_serializable: ^6.1.5
+  json_serializable: ^6.2.0
   grinder: ^0.9.0
   flutter_lints: ^1.0.0
 flutter: