master_ssl_verify_server_cert value is not set correctly

An MDEV to cover for the bug reported as https://github.com/MariaDB/server/pull/4880:

Description

In MariaDB 12.3.1, MariaDB made this change to refactor ssl_verify_server_cert to master_ssl_verify_server_cert in commit 89bd6b0.

However, these values are different types. While ssl_verify_server_cert is my_bool type, the master_ssl_verify_server_cert is trilean type which accepts three possible values (Yes/No/Default). When reading the value of the argument using !(my_bool)arg in mysql_options, trilean type value can't be retrieved because it accesses the wrong memory address by just passing the master_ssl_verify_server_cert, causing the master_ssl_verify_server_cert still behaves as "ON" when it's set to "OFF".

This commit changes the implementation to master_ssl_verify_server_cert.value to retrieve the correct value.

How can this PR be tested?

Execute MTR test rpl_ssl_verify_server_cert_trilean_bug in the rpl suite.