Import of xarray conda package fails for 0.21

[constantinpape]

It appears that the latest xarray conda package (0.21) does not pull in all the necessary dependencies.
One of our conda-forge builds fails when importing xarray:

    import xarray as xr
  File "/home/conda/feedstock_root/build_artifacts/bioimageio.core_1643501164132/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_/lib/python3.10/site-packages/xarray/__init__.py", line 1, in <module>
    from . import testing, tutorial, ufuncs
  File "/home/conda/feedstock_root/build_artifacts/bioimageio.core_1643501164132/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_/lib/python3.10/site-packages/xarray/testing.py", line 8, in <module>
    from xarray.core import duck_array_ops, formatting, utils
  File "/home/conda/feedstock_root/build_artifacts/bioimageio.core_1643501164132/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_/lib/python3.10/site-packages/xarray/core/duck_array_ops.py", line 24, in <module>
    from . import dask_array_compat, dask_array_ops, dtypes, npcompat, nputils
  File "/home/conda/feedstock_root/build_artifacts/bioimageio.core_1643501164132/_test_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_/lib/python3.10/site-packages/xarray/core/dask_array_compat.py", line 4, in <module>
    from packaging.version import Version
ModuleNotFoundError: No module named 'packaging

Pinning xarray to a version <0.21 removes this issue.
See conda-forge/bioimageio.core-feedstock#15 (comment) for more context.

[jhamman]

See pydata/xarray#6207 for fix in-progress.