Ray workflow fails due to new ray version

[jpata]

The ray test now crashes with the following (it fails despite being called a warning):

DeprecationWarning: The environment variable `RAY_AIR_LOCAL_CACHE_DIR` is deprecated. It is no longer used and will not have any effect. You should set the `storage_path` instead. Files will no longer be written to `~/ray_results` as long as `storage_path` is set.See the docs: https://docs.ray.io/en/latest/train/user-guides/persistent-storage.html#setting-the-local-staging-directory

It's used here:

$ git grep RAY_AIR_LOCAL_CACHE_DIR
mlpf/pyg/training.py:    os.environ["RAY_AIR_LOCAL_CACHE_DIR"] = tmp_ray_cache.name
mlpf/pyg/training.py:    _logger.info(f"RAY_AIR_LOCAL_CACHE_DIR: {os.environ['RAY_AIR_LOCAL_CACHE_DIR']}")
mlpf/pyg/training.py:    os.environ["RAY_AIR_LOCAL_CACHE_DIR"] = tmp_ray_cache.name
mlpf/pyg/training.py:    _logger.info(f"RAY_AIR_LOCAL_CACHE_DIR: {os.environ['RAY_AIR_LOCAL_CACHE_DIR']}")

I disabled ray for now in 4cc9adbddd805267f8ef3ee2b1f302c2d460cc17, but it would be good to update the code to match the latest ray version.