chore(docs): fix runnable example (langchain-ai#9027)

Author: hntrl

docs/core_docs/docs/how_to/assign.ipynb

@@ -36,7 +36,7 @@
     },
     {
       "cell_type": "code",
-      "execution_count": 1,
+      "execution_count": null,
       "metadata": {},
       "outputs": [
         {
@@ -56,8 +56,8 @@
         "const runnable = RunnableParallel.from({\n",
         "  extra: RunnablePassthrough.assign({\n",
         "    mult: (input: { num: number }) => input.num * 3,\n",
-        "    modified: (input: { num: number }) => input.num + 1\n",
-        "  })\n",
+        "  }),\n",
+        "  modified: (input: { num: number }) => input.num + 1,\n",
         "});\n",
         "\n",
         "await runnable.invoke({ num: 1 });"