`test_mitgcm` test failing with new dask release

`docs/examples/example_dask_chunk_OCMs.py::test_mitgcm` has been failing in CI this week with the release of dask [`v2024.11.0`](https://docs.dask.org/en/stable/changelog.html#v2024-11-1).

Downgrading to v2024.10.0 fixes the error, but it would be good to investigate and patch the test.