Fix re.split DeprecationWarning

[jamesjer]

Silences this DeprecationWarning with python 3.13.0b2:

  /builddir/build/BUILD/python-jupytext-1.16.2-build/BUILDROOT/usr/lib/python3.13/site-packages/jupytext/cell_metadata.py:260: DeprecationWarning: 'maxsplit' is passed as positional argument
    options = re.split(r"\s|,", options, 1)

[github-actions[bot]]

Thank you for making this pull request.

Did you know? You can try it on Binder: or .

Also, the version of Jupytext developed in this PR can be installed with pip:

HATCH_BUILD_HOOKS_ENABLE=true pip install git+https://github.com/jamesjer/jupytext.git@main

(this requires nodejs, see more at Developing Jupytext)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.73%. Comparing base (42a48e8) to head (89c450e). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1241 +/- ## ======================================= Coverage 97.73% 97.73% ======================================= Files 29 29 Lines 4468 4468 ======================================= Hits 4367 4367 Misses 101 101 ``` | [Flag](https://app.codecov.io/gh/mwouts/jupytext/pull/1241/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Marc+Wouts) | Coverage Δ | | |---|---|---| | [external](https://app.codecov.io/gh/mwouts/jupytext/pull/1241/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Marc+Wouts) | `75.14% <100.00%> (+0.09%)` | :arrow_up: | | [functional](https://app.codecov.io/gh/mwouts/jupytext/pull/1241/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Marc+Wouts) | `88.52% <100.00%> (ø)` | | | [integration](https://app.codecov.io/gh/mwouts/jupytext/pull/1241/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Marc+Wouts) | `77.28% <100.00%> (ø)` | | | [unit](https://app.codecov.io/gh/mwouts/jupytext/pull/1241/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Marc+Wouts) | `66.56% <100.00%> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Marc+Wouts#carryforward-flags-in-the-pull-request-comment) to find out more.

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[mwouts]

Thank you @jamesjer for the fix!