Docs: Build with Sphinx --pre release

[humitos]

If a Requirement specifier includes a pre-release or development
version (e.g. >=0.0.dev0) then pip will allow pre-release and development
versions for that requirement. This does not include the != flag.

From https://pip.pypa.io/en/latest/cli/pip_install/#pre-release-versions

Do not merge this PR, it's just a test to build the theme with Sphinx --pre release

Edit: I did this as an example for sphinx-doc/sphinx#9088 (comment)

[Blendify]

I guess this should be used with #1123?

[humitos]

@Blendify I added this as an example of sphinx-doc/sphinx#9088 (comment)

I don't think we want to add this to master for building our docs. However, it may be a good idea to add it to the Sphinx versions that are used to test our theme so we can find issues on our theme before the release is done.

[humitos]

@ericholscher One failure that I found is that this page breaks: https://sphinx-rtd-theme--1130.org.readthedocs.build/en/1130/demo/demo.html. The table of content does not render properly.

See the original: https://sphinx-rtd-theme.readthedocs.io/en/stable/demo/demo.html

It seems the CSS selector is too specific based on .section class that it was replaced by a <section> html tag in docutils==0.17

[Blendify]

Can this be closed now?

[humitos]

Yes. Let's close it. It was a test for the pre-release of Sphinx.

However, we should probably create an automated way of building our theme with the latest pre-release of Sphinx to detect breaking changes earlier.