It comes when checking python3 version that is "3.10.2+", and it's that "2+" that it's complaining about.
Will push even to S2_6
As we don't check python version number in S3_0, this is not currently breaking build on that branch -> no need to "emergency" freeciv-3.0 release.
Running build test set (S3_1) on Ubuntu-22.04 development version prints out "Illegal number" errors from autogen.sh.
This is most likely some version number in the system containing non-numeral part that autogen.sh regardless tries to treat as number.