x11-servers/xorg-server: update to 21.1.20

This fixes open CVEs CVE-2025-62229, CVE-2025-62230, and CVE-2025-62231.

Reported by: rob2g2-freebsd@bitbert.com
PR: 290655
Security: e99a32c8-b8e2-11f0-8510-b42e991fc52e
MFH: 2025Q4
Approved by: x11 (maintainer timeout)

(cherry picked from commit 34de5acb0688621eca69ddf0e55f9a928525e199)