Incorrect minimum dependency on xarray.

[jenshnielsen]

Following the merge of #556 and release in 0.10.1 cf_xarray imports xarray.groupers via from xarray.groupers import EncodedGroups, UniqueGrouper support for this was added in xarray 2024.07.0 via https://github.com/pydata/xarray/pull/9289. However the minumum dependency given here is still "xarray>=2022.03.0",. This results in test failures in my project that depends on both xarray and cf_xarray since an incorrect resolution is performed. If possible it would be nice to test cf_xarray against the minimum specified version of xarray in the future