20181108 is the version used by the current Debian oldstable.
Ubuntu 20.04 LTS has 20191020.
pdfminer installs cryptography, >= 38 breaks pyOpenSSL < 22 as found in
Ubuntu 20.04 LTS. Update docs job to use ubuntu-22.04 to avoid
failures.
With Python 3.7 and Requests 2.4.0 on Ubuntu 20.04 there are two test
failures; reasons not immediately clear. There is a warning for the use
of ABCs from collections and not collections.abc. That will cause an
exception on Python 3.10 and is fixed in Requests 2.19.0.
