RefEx section - Dataflow API error: The job graph is too large

Congrats on the impressive SoTA results! 🥇

In following the steps to reproduce the tests, I stumbled into a couple of issues. Some were easy to resolve, but the one below is a blocker. Any suggestions would be appreciated. 🙏🏼

The data prep step in the RefEx section fails with the error below:

```
python -m pix2struct.preprocessing.convert_refexp --data_dir=$PIX2STRUCT_DIR/data/refexp --image_dir=$PIX2STRUCT_DIR/data/rico_images -- --runner=DataflowRunner --save_main_session --project=$GCP_PROJECT --region=$GCP_REGION --temp_location=$PIX2STRUCT_DIR/data/temp --staging_location=$PIX2STRUCT_DIR/data/staging --setup_file=./setup.py
```

```
File "/home/gitpod/miniconda3/envs/pix2struct/lib/python3.9/site-packages/apitools/base/py/base_api.py", line 737, in ProcessHttpResponse
self.__ProcessHttpResponse(method_config, http_response, request))
File "/home/gitpod/miniconda3/envs/pix2struct/lib/python3.9/site-packages/apitools/base/py/base_api.py", line 603, in __ProcessHttpResponse
raise exceptions.HttpError.FromResponse(
apitools.base.py.exceptions.HttpBadRequestError: HttpError accessing : response: <{'vary': 'Origin, X-Origin, Referer', 'content-type': 'application/json; charset=UTF-8', 'date': 'Sat, 31 Dec 2022 03:21:02 GMT', 'server': 'ESF', 'cache-control': 'private', 'x-xss-protection': '0', 'x-frame-options': 'SAMEORIGIN', 'x-content-type-options': 'nosniff', 'transfer-encoding': 'chunked', 'status': '400', 'content-length': '228', '-content-encoding': 'gzip'}>, content <{
"error": {
"code": 400,
"message": "(634623baaa978ce): The job graph is too large. Please try again with a smaller job graph, or split your job into two or more smaller jobs.",
"status": "INVALID_ARGUMENT"
}
}
>
```