security/vuxml: add security/openvpn[-devel] vuln entries.

Aligned with Gert Doering for openvpn-devel.

PR: 296429
Security: ffa897a0-756f-11f1-b291-a74de6bb0320
Security: CVE-2026-11771
Security: CVE-2026-12932
Security: CVE-2026-12996
Security: CVE-2026-13117
Security: CVE-2026-13122
Security: CVE-2026-13698

Pull Request: https://github.com/freebsd/freebsd-ports/pull/550