Update sphinx to 3.5.4

[pyup-bot]

This PR updates Sphinx from 3.5.3 to 3.5.4.

Changelog

3.5.4

=====================================

Dependencies
------------

* 9071: Restrict docutils to 0.16

Bugs fixed
----------

* 9078: autodoc: Async staticmethods and classmethods are considered as non
async coroutine-functions with Python3.10
* 8870, 9001, 9051: html theme: The style are not applied with docutils-0.17

- toctree captions
- The content of ``sidebar`` directive
- figures

Links

• PyPI: https://pypi.org/project/sphinx
• Changelog: https://pyup.io/changelogs/sphinx/
• Homepage: http://sphinx-doc.org/

[pyup-bot]

Closing this in favor of #88