Print a more user-friendly error when tls-crypt-v2 client auth fails

Print a more user-friendly error when tls-crypt-v2 client auth fails

While it might be clear to people being (too?) well versed in
typical crypto applications that an authentication failure probably
mean wrong decryption key, this is not really obvious for the typical
user/server admin.

Change-Id: If0f0e7d53f915d39ab69aaaac43dc73bb9c26ae9
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20230522091231.2837468-1-arne@rfc2549.org>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg26718.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 7a477c16a7c2a7016c7b15ea98fe3c40e8ef675b)