Fix Test_to_zarr_split:

[jbusecke]

          There is a weird error here [when comparing the zarr metadata](https://github.com/ocean-transport/scale-aware-air-sea/actions/runs/9070237187/job/24921584485#step:5:313) written as splits and written with vanilla xarray. I will raise a separate issue to track this (it should not influence our paper at all) and deal with it later.

Originally posted by @jbusecke in #61 (comment)