Fix mypy issue

[BSchilperoort]

Great. The mypy failure seems to be real, although unrelated to this PR. I reran the docs build which went through.

Something must have changed in a dependency. If I create a new environment from scratch, I can reproduce the error.

For some reason mypy things dy on this line is of type str | Unknown, because of the .item() call.

xarray-regrid/src/xarray_regrid/utils.py

Line 314 in 8411437

dy = obj.coords[lat_coord].diff(lat_coord).max().values.item()

Changing this to;

    dy: Any = obj.coords[lat_coord].diff(lat_coord).max().values.item() 

makes mypy happy again :/

Originally posted by @BSchilperoort in #59 (comment)