lists: install python3-python if there is no python-base

Package python-base was providing python link to python2. By removing python-base (and effectively this way Python2) from system this removes this link as well. This link is commonly expected to be present so we add it for python3 if there is not python-base.

This condition also as corner case support case when Python3 is not installed.

This is companion for https://gitlab.labs.nic.cz/turris/turris-os-packages/-/merge_requests/341