Fixes https://github.com/certbot/certbot/issues/8400.
I had to switch the package installed in `apacheconftest` to `libapache2-mod-wsgi-py3` because Ubuntu 20.10 removed the Python 2 version of this module.
I didn't add this AMI to `tests/letstest/auto_targets.yaml` because like Ubuntu 20.04, `certbot-auto` has never worked on the OS.
* Add Ubuntu 20.20 test farm tests
* Try Python 3 WSGI