`test_array_object.py::test_getitem_masking` relies on shape assertion

`test_array_object.py::test_getitem_masking` fails in Dask due to a `assert_shape` call on a masked array. This should be hidden behind the `--disable-data-dependent-shapes` flag.

See https://github.com/tomwhite/dask/runs/5306535598?check_suite_focus=true