adapt the pint + dask test to the newest version of pint (#7855)

* use the registry to create the quantities

* skip the `pint` + `dask` test before `pint=0.21`

* also parse the static version

xarray/tests/test_units.py

@@ -5627,16 +5627,20 @@ def test_merge(self, variant, unit, error, dtype):
 
 @requires_dask
 class TestPintWrappingDask:
+    @pytest.mark.skipif(
+        version.parse(pint.__version__) <= version.parse("0.21"),
+        reason="pint didn't support dask properly before 0.21",
+    )
     def test_duck_array_ops(self):
         import dask.array
 
         d = dask.array.array([1, 2, 3])
-        q = pint.Quantity(d, units="m")
+        q = unit_registry.Quantity(d, units="m")
         da = xr.DataArray(q, dims="x")
 
         actual = da.mean().compute()
         actual.name = None
-        expected = xr.DataArray(pint.Quantity(np.array(2.0), units="m"))
+        expected = xr.DataArray(unit_registry.Quantity(np.array(2.0), units="m"))
 
         assert_units_equal(expected, actual)
         # Don't use isinstance b/c we don't want to allow subclasses through