test_save_mfdataset_compute_false_roundtrip fails

What happened:

test_save_mfdataset_compute_false_roundtrip consistently fails in windows-latest-3.9, e.g. https://github.com/pydata/xarray/pull/5244/checks?check_run_id=2485202784

Here's the traceback:

self = <xarray.tests.test_backends.TestDask object at 0x000001FF45A9B640>

    def test_save_mfdataset_compute_false_roundtrip(self):
        from dask.delayed import Delayed
    
        original = Dataset({"foo": ("x", np.random.randn(10))}).chunk()
        datasets = [original.isel(x=slice(5)), original.isel(x=slice(5, 10))]
        with create_tmp_file(allow_cleanup_failure=ON_WINDOWS) as tmp1:
            with create_tmp_file(allow_cleanup_failure=ON_WINDOWS) as tmp2:
                delayed_obj = save_mfdataset(
                    datasets, [tmp1, tmp2], engine=self.engine, compute=False
                )
                assert isinstance(delayed_obj, Delayed)
                delayed_obj.compute()
                with open_mfdataset(
                    [tmp1, tmp2], combine="nested", concat_dim="x"
                ) as actual:
>                   assert_identical(actual, original)
E                   AssertionError: Left and right Dataset objects are not identical
E                   
E                   
E                   Differing data variables:
E                   L   foo      (x) float64 dask.array<chunksize=(5,), meta=np.ndarray>
E                   R   foo      (x) float64 dask.array<chunksize=(10,), meta=np.ndarray>

Anything else we need to know?:

xfailed in https://github.com/pydata/xarray/pull/5245

Environment:

[Eliding since it's the test env]

Start with xarray.tests.test_backends.TestDask.test_save_mfdataset_compute_false_roundtrip and the linked Windows CI failure. Reproduce it on windows-latest-3.9, then inspect the save_mfdataset/open_mfdataset roundtrip behavior and the xfailed case in pull request 5245. Done means the test passes and the roundtripped dataset is identical to the original.