fix: update event handling to use event.arguments instead of event.source

Author: arnabrahman

packages/event-handler/src/appsync-graphql/AppSyncGraphQLResolver.ts

@@ -266,7 +266,7 @@ class AppSyncGraphQLResolver extends Router {
       const results: unknown[] = [];
       for (const event of events) {
         const result = await handler.apply(resolveOptions?.scope ?? this, [
-          event.source as Record<string, unknown>,
+          event.arguments,
           { event, context },
         ]);
         results.push(result);
@@ -279,7 +279,7 @@ class AppSyncGraphQLResolver extends Router {
       const event = events[idx];
       try {
         const result = await handler.apply(resolveOptions?.scope ?? this, [
-          event.source as Record<string, unknown>,
+          event.arguments,
           { event, context },
         ]);
         results.push(result);