fix: json_serializableのバージョンを6.10.0から6.9.0にダウングレード

Author: LibraryLibrarian

pubspec.yaml

@@ -34,7 +34,7 @@ dev_dependencies:
     sdk: flutter
   flutter_lints: ^5.0.0
   build_runner: ^2.7.0
-  json_serializable: ^6.10.0
+  json_serializable: 6.9.0
   file: ^7.0.1
 
 # For information on the generic Dart part of this file, see the