Use newer OpenSSL version for sphinx documentation compilation

Both the Allen and Moore documentation pipelines fail in master since a few days. See for example

https://gitlab.cern.ch/lhcb/Allen/-/jobs/29328974 https://gitlab.cern.ch/lhcb/Moore/-/jobs/29344431

This is possibly linked to a new version of urllib3 from May 2nd, since the pipelines fail since then. From the error message it looks like we need a newer version of ssl, supporting at least OpenSSL version 1.1.0. That would mean ssl 3.5.3 (https://docs.python.org/3/library/ssl.html).