textproc/libxml2: Update to 2.11.8

Fixes CVE-2024-34459

Reference:
https://www.cve.org/CVERecord?id=CVE-2024-34459

Changelog:
https://gitlab.gnome.org/GNOME/libxml2/-/releases/v2.11.8

PR: 279043
Approved by: desktop (tcberner)
Sponsored by: Blinkinblox
Exp-run by: antoine