@meeseeksdev backport to v4.3.x

@meeseeksdev backport to v4.0.x

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v4.0.x
$ git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 642d8aea136d274a82928a8735cd25d6905116ed

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #11724: DOC: Pin max version of Sphinx'

4. Push to a named branch :

git push YOURFORK v4.0.x:auto-backport-of-pr-11724-on-v4.0.x

5. Create a PR against branch v4.0.x, I would have named this PR:

"Backport PR #11724 on branch v4.0.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.

Backport updates:

• backport to 4.3.x is done by the bot at Backport PR #11724 on branch v4.3.x (DOC: Pin max version of Sphinx) #11799
• backport to 4.0.x was done directly by me via d620647

This should at least temporarily fix the associated RTD failure that would block subsequent backports.

p.s. 4.0.x seems to be broken by other things too...

Because of the custom commit message on v4.0.x the consistency scripts don't pick it up so I'll mark this as a manual backport.