chore(deps): update json_serializable version constraint to match our sdk constraint

Author: Fluf22

templates/dart/pubspec.mustache

@@ -26,7 +26,7 @@ dependencies:
 
 dev_dependencies:
   build_runner: ^2.4.7
-  json_serializable: '>=6.0.0 <6.12.0'
+  json_serializable: '>=6.0.0 <6.9.0'
   lints: ^6.0.0
   logging: ^1.2.0
   test: ^1.25.8