Fix formatting of training_dataset line in notebook (#5709)

Author: thvasilo

v3-examples/model-customization-examples/rlvr_finetuning_example_notebook_v3_prod.ipynb

@@ -145,7 +145,7 @@
     "    model_package_group=model_package_group, # or use an existing model package group arn\n",
     "    mlflow_experiment_name=\"test-rlvr-finetuned-models-exp\", \n",
     "    mlflow_run_name=\"test-rlvr-finetuned-models-run\", \n",
-    "    training_dataset=dataset.arn\n",
+    "    training_dataset=dataset.arn,\n",
     "    s3_output_path=\"s3://mc-flows-sdk-testing/output/\",\n",
     "    accept_eula=True\n",
     ")"