[PATCH] docs: prevent build error by rolling back Sphinx version

[Stephen Finucane]

On Mon, 2021-08-23 at 16:48 +1000, Daniel Axtens wrote:
> We're hitting a sphinxcontrib-httpdomain vs sphinx issue that was
> causing the openapi part of doc builds to error out with:
> 
> <openapi>:1:Problem in http domain: field is supposed to use role 'obj', but that role is not in the domain.
> 
> See https://github.com/sphinx-contrib/httpdomain/pull/51
> 
> Until it's fixed, hold back the Sphinx version to < 4.1.0
> 
> Signed-off-by: Daniel Axtens <dja at axtens.net>

Unfortunate but necessary. The gate for sphinx-contrib/httpdomain is pretty
badly broken right now so it could be a while before that patch lands :-(

Reviewed-by: Stephen Finucane <stephen at that.guru>

...and applied.

Stephen