Not passing `interp` kwargs to `DataArray.interp`

[martijnvandermarel]

https://github.com/xarray-contrib/pint-xarray/blob/ca4e282dda63c5b3ea39b9743fbf7165506b8e72/pint_xarray/accessors.py#L754

From the documentation it seems the kwargs argument is meant to be passed unmodified to xarray's DataArray.interp method. However from the line above it doesn't seem to do that.

The same goes for the assume_sorted argument by the way.