Upstream xarray causing build to fail with "ValueError: unmatched dimensions for multi-index variables"

[tomwhite]

From https://github.com/pystatgen/sgkit/runs/6213029601?check_suite_focus=true:

=================================== FAILURES ===================================
________________________ test_variables_in_multi_index _________________________

dummy_ds = <xarray.Dataset>
Dimensions:  (d1: 3, bar: 3)
Coordinates:
  * bar      (bar) int64 1 2 3
Dimensions without coordinates: d1
Data variables:
    foo      (d1) int64 1 2 3

    def test_variables_in_multi_index(dummy_ds: xr.Dataset) -> None:
        # create a multi index
>       ds = dummy_ds.set_index({"ind": ("foo", "bar")})

sgkit/tests/test_variables.py:98: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/opt/hostedtoolcache/Python/3.9.12/x64/lib/python3.9/site-packages/xarray/core/dataset.py:3766: in set_index
    idx, idx_vars = PandasMultiIndex.from_variables_maybe_expand(
/opt/hostedtoolcache/Python/3.9.12/x64/lib/python3.9/site-packages/xarray/core/indexes.py:660: in from_variables_maybe_expand
    _check_dim_compat({**current_variables, **variables})
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

variables = {'bar': <xarray.IndexVariable 'bar' (bar: 3)>
array([1, 2, 3]), 'foo': <xarray.Variable (d1: 3)>
array([1, 2, 3])}
all_dims = 'equal'

    def _check_dim_compat(variables: Mapping[Any, Variable], all_dims: str = "equal"):
        """Check that all multi-index variable candidates are 1-dimensional and
        either share the same (single) dimension or each have a different dimension.
    
        """
        if any([var.ndim != 1 for var in variables.values()]):
            raise ValueError("PandasMultiIndex only accepts 1-dimensional variables")
    
        dims = {var.dims for var in variables.values()}
    
        if all_dims == "equal" and len(dims) > 1:
>           raise ValueError(
                "unmatched dimensions for multi-index variables "
                + ", ".join([f"{k!r} {v.dims}" for k, v in variables.items()])
            )
E           ValueError: unmatched dimensions for multi-index variables 'foo' ('d1',), 'bar' ('bar',)

/opt/hostedtoolcache/Python/3.9.12/x64/lib/python3.9/site-packages/xarray/core/indexes.py:491: ValueError
=========================== short test summary info ============================
FAILED sgkit/tests/test_variables.py::test_variables_in_multi_index - ValueEr...
= 1 failed, 826 passed, 32 skipped, 2 xfailed, 1 xpassed in 243.48s (0:04:03) ==

[tomwhite]

This started failing after #5692 went in.