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 34de5acb)