openvpn: update to 2.6.12

openvpn: update to 2.6.12

This is a bugfix release

Bug fixes:

 - the fix for CVE-2024-5594 (refuse control channel messages with nonprintable characters) was too strict, breaking user configurations
   with AUTH_FAIL messages having trailing CR/NL characters. This often happens if the AUTH_FAIL reason is set by a script.

 - Http-proxy: fix bug preventing proxy credentials caching

For details refer to https://github.com/OpenVPN/openvpn/blob/v2.6.12/Changes.rst

Signed-off-by: Ivan Pavlov <AuthorReflex@gmail.com>