wip with unpublished json_serializable

Author: kevmoo

functions_framework/lib/src/cloud_event.g.dart

@@ -25,3 +25,7 @@ dev_dependencies:
   # Because we use the ignore_for_file build.yaml config
   source_gen: ^1.0.0
   test: ^1.15.7
+
+dependency_overrides:
+  json_serializable:
+    path: ../../json_serializable/json_serializable