Fix expected format

Author: TartanLlama

integration-tests/js-compute/fixtures/module-mode/tests.json

@@ -147,7 +147,7 @@
   "GET /hono": {
     "downstream_response": {
       "status": 200,
-      "body_prefix": "{\n  \"args\": {},"
+      "body_prefix": "{\n  \"args\": \"\","
     }
   },
   "GET /http-cache/hook-errors": {