Xarray v2024.03 changes array behaviour

[brynpickering]

Noticed a change in xarray behaviour in a failing PR run that installed v2024.03: https://github.com/arup-group/genet/actions/runs/8471718196/job/23332569549?pr=232

The error being raised is about a newly introduced .oindex property, but I think there is a general issue with how arrays are being loaded as datasets. This could extend to rioxarray or how we are storing processed elevation data on disk.

Fix for now: pin to < v2024.03 (see #236).