remove xfail from `test_dataarray.test_to_dask_dataframe()`

[dcherian]

What is your issue?

when dask-expr is fixed. Added in #8837

[mathause]

Won't pandas 3 enforce COW and we have to fix this differently? (not 100% sure, though) pandas 3 is planned for April pandas-dev/pandas#57064

[dcherian]

This is a different issue: dask/dask-expr#981