Use require_serial: true as the default for our pre-commit hook, not -j1

[AlexWaygood]

Currently we have [--jobs=1] as the default args for our pre-commit hook. This is problematic, however, as repos that override args in their .pre-commit-config.yaml files (such as CPython) have to re-specify -j1 in their args: the value they provide for args overrides the default we give here rather than extending it.

This PR proposes that we don't give a default value for args, and instead give a default value for the require_serial key. Testing locally, using require_serial: true does seem to be slightly slower than using --jobs=1 for me. But the difference is barely perceptible, and I think this is a big usability improvement: it means we don't have to document that, if you're overriding args in your .pre-commit.config.yaml file, you'll need to make sure to add --jobs=1 in your override.

[AlexWaygood]

I'll do a patch release with this in it

[AlexWaygood]

https://pypi.org/project/sphinx-lint/0.8.1/

[AlexWaygood]

Looks like this approach is also what black does for its pre-commit hook (black being another Python tool that uses multiprocessing internally): https://github.com/psf/black-pre-commit-mirror/blob/main/.pre-commit-hooks.yaml