Bring minimum Python version in line with minimum Meson version
Follow-up to #44735. As discussed there, starting with freeciv-3.3, the minimum Python version required for the autotools build should follow the minimum Python version required for the minimum Meson version for the meson build (at the time of writing, that's Python 3.6). This ticket is about increasing the Python requirement appropriately for the first time, once S3_2 branching (#44374) is done.
Another kind of data point to the discussion:
Python2 may be long EOL by the upstream. Yet, when I try to install latest VirtualBox development snapshot (as the latest release does not work with the 5.18 kernel my system is now running), the installation script says: "Python 2 (2.6 or 2.7) not available, skipping bindings installation."