Revert downstream-CI fix for earthkit 1.0

[mcocdawc]

What maintenance does this project need?

In ecmwf/downstream-ci#79
we removed the dependency on earthkit for anemoi, because the 1.0 release version is not compatible (yet).

Re-enable this dependency.

Organisation

ecmwf

[github-actions]

This issue has been marked as inactive due to inactivity. It will be closed if no further activity occurs in the next 10 days.