Align Sphinx requirement with our RTD instance

[pauloxnet]

Even though in Django pipelines we do not generate documentation but we only check typos, I remembered that we also generate documentation on RTD https://django.readthedocs.io

I verified that the builds run on Ubuntu 20.04 and Python 3.8
https://github.com/django/django/blob/main/.readthedocs.yml

You can see from the logs that the latest versions of Sphinx, docutils and babel compatible with Python 3.8 are installed
https://app.readthedocs.org/projects/django/builds/25876554/#246564223--78

For this reason I drafted the PR #1694 that is blocked by the Python 3.8 drop and opened this one that can be merged immediately since, from what already happens on RTD we already know that everything works well (in addition to the local tests)

[bmispelon]

Hi @pauloxnet, thanks for all the PRs you're sending lately ✨
Could you stop requesting reviews from the ops team unless it's strictly needed (it's generating a lot of notifications). For things like this one, I think asking the site maintainers is enough.

Thanks!

[pauloxnet]

Hi @pauloxnet, thanks for all the PRs you're sending lately ✨ Could you stop requesting reviews from the ops team unless it's strictly needed (it's generating a lot of notifications). For things like this one, I think asking the site maintainers is enough.

Yes, of course, sorry for all the notifications.

Actually, when I tagged you I thought that PR was relevant for the ops team, but I will tag you only when strictly necessary.

To avoid further notifications, I take advantage of this comment to ask you what version of Debian/Ubuntu/Dockeriamge do we use for the website server?