security/openvpn: security update to 2.6.7

PR: 275055
Changelog: https://github.com/OpenVPN/openvpn/blob/v2.6.7/Changes.rst#overview-of-changes-in-267
Security: CVE-2023-46849
Security: CVE-2023-46850
MFH: 2023Q4
(cherry picked from commit 03b2c6723f872fdfe5f0ea88bc97e6a7374c48ac)