6001240_labels.zarr missing version key in labels group

[dstansby]

The 6001240_labels.zarr IDR dataset (NGFF-validator link) has the following labels/zarr.json:

{
  "attributes": {
    "ome": {
      "labels": [
        "0"
      ]
    }
  },
  "zarr_format": 3,
  "node_type": "group"
}

This is missing the "ome" > "version" key, so I don't think is valid OME-Zarr metadata.

I opened a 'sibiling' issue for the NGFF validator at ome/ome-ngff-validator#66 since it's not coming up as an error there.