roundtripping bytes with specific _FillValue fails on Zarr 3.0.7

[dcherian]

What happened?

Seen in CI. I have xfailed the Zarr test in #10255

xarray/tests/test_backends.py::TestZarrDictStore::test_roundtrip_bytes_with_fill_value[2]: AssertionError: Left and right Dataset objects are not identical
Differing data variables:
L   x        (t) object 24B b'ab' b'cdef' nan
R   x        (t) object 24B b'ab' b'cdef' b'X'
xarray/tests/test_backends.py::TestZarrDirectoryStore::test_roundtrip_bytes_with_fill_value[2]: AssertionError: Left and right Dataset objects are not identical
Differing data variables:
L   x        (t) object 24B b'ab' b'cdef' nan
R   x        (t) object 24B b'ab' b'cdef' b'X'
xarray/tests/test_backends.py::TestZarrWriteEmpty::test_roundtrip_bytes_with_fill_value[2]: AssertionError: Left and right Dataset objects are not identical
Differing data variables:
L   x        (t) object 24B b'ab' b'cdef' nan
R   x        (t) object 24B b'ab' b'cdef' b'X'

This is probably an upstream issue, zarr-developers/zarr-python#2979 but we should remember to remove the xfail when upstream is fixed.

cc @ianhi