games/freeciv21: Update 3.1.0 => 3.1.1

This is a security release:
https://github.com/longturn/freeciv21/security/advisories/GHSA-f76g-6w3f-f6r3

Changelog:
https://github.com/longturn/freeciv21/releases/tag/v3.1.1

PR: 293964
Approved by: makc (mentor)