To upgrade Sphinx, MyST-Parser and markdown-it-py must also be updated at the
same time:

Closes: https://github.com/searxng/searxng/pull/2433
Closes: https://github.com/searxng/searxng/pull/2492
Closes: https://github.com/searxng/searxng/pull/2504


Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>