Pin to sphinx<9

[weiji14]

Workaround for AttributeError: type object 'Autosummary' has no attribute 'create_documenter'.

Xref xarray-contrib/sphinx-autosummary-accessors#165

[weiji14]

Another error on the readthedocs build - https://app.readthedocs.org/projects/cupy-xarray/builds/31669682/:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/sphinx/config.py", line 529, in eval_config_file
    exec(code, namespace)  # NoQA: S102
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/checkouts/82/docs/conf.py", line 11, in <module>
    import cupy_xarray  # noqa: F401
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/checkouts/82/cupy_xarray/__init__.py", line 2, in <module>
    from .accessors import CupyDataArrayAccessor, CupyDatasetAccessor  # noqa
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/checkouts/82/cupy_xarray/accessors.py", line 5, in <module>
    import cupy as cp
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/cupy/__init__.py", line 18, in <module>
    from cupy import _core  # NOQA
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/cupy/_core/__init__.py", line 5, in <module>
    from cupy._core import core  # NOQA
  File "cupy/_core/core.pyx", line 1, in init cupy._core.core
  File "cupy/_core/_routines_math.pyx", line 7, in init cupy._core._routines_math
  File "cupy/_core/_reduction.pyx", line 1, in init cupy._core._reduction
  File "cupy/_core/_cub_reduction.pyx", line 260, in init cupy._core._cub_reduction
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/cupy/_environment.py", line 86, in get_nvcc_path
    _nvcc_path = _get_nvcc_path()
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/cupy/_environment.py", line 198, in _get_nvcc_path
    cuda_path = get_cuda_path()
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/cupy/_environment.py", line 78, in get_cuda_path
    _cuda_path = _get_cuda_path()
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/cupy/_environment.py", line 151, in _get_cuda_path
    conda_cuda_path = _get_conda_cuda_path()
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/site-packages/cupy/_environment.py", line 130, in _get_conda_cuda_path
    cuda_path = os.path.join(conda_prefix, 'targets', arch)
  File "/home/docs/checkouts/readthedocs.org/user_builds/cupy-xarray/conda/82/lib/python3.10/posixpath.py", line 76, in join
    a = os.fspath(a)
TypeError: expected str, bytes or os.PathLike object, not NoneType

I see a similar error reported at cupy/cupy#9698 (comment), but not sure if it's related. Don't really want to pin cupy-core 🙃 Edit: proper bug report at cupy/cupy#9777

[jacobtomlinson]

Instead of constraining this here maybe it would be better to patch the conda-forge repo metadata for the sphinx-autosummary-accessors to limit to sphinx<9 there? cc @keewis

[keewis]

I won't have time to constrain the repo metadata in the near future (and a proper fix appears to require changes to sphinx first, so that will take even more work), but feel free to do that on my behalf if you like.

However, I do think that constraining locally is the right move in this case.