Since the release of `sphinx 4.1`, a new warning related to `httpdomain`
extension appeared when buidling `swh-web` documentation.
It is not critical and is due to httpdomain not in sync with latest
changes in sphinx, so filter out that warning as it makes sphinx
builds fail for swh-web on Jenkins.
A [pull request](https://github.com/sphinx-contrib/httpdomain/pull/51) has been created to fix the issue,
the introduced hack should be remove if it gets merged and a new
`sphinx-httpdomain` version released.