[`GroupMetadataV2`](https://github.com/zarr-developers/zarr-python/blob/7c2f372f21b2555e11b2ab52f0e659a0306e5741/packages/zarr-metadata/src/zarr_metadata/v2/group.py#L11) doesn't have an `attributes` key, but `ArrayMetadataV2` [does](https://github.com/zarr-developers/zarr-python/blob/7c2f372f21b2555e11b2ab52f0e659a0306e5741/packages/zarr-metadata/src/zarr_metadata/v2/array.py#L65). The fix is to add an `attributes` field to `GroupMetadataV2`.
GroupMetadataV2doesn't have anattributeskey, butArrayMetadataV2does.The fix is to add an
attributesfield toGroupMetadataV2.