Fix too greedy disable of the MySQL server cert verification

Before, it was sufficient to set ssl_do_not_verify_server_cert to any value.
Now it is necessary to set a value that is not considered empty().

src/Adapter/Mysql.php

@@ -46,7 +46,7 @@ public function getOptions(Config $config)
 
             if (
                 defined('PDO::MYSQL_ATTR_SSL_VERIFY_SERVER_CERT')
-                && isset($config->ssl_do_not_verify_server_cert)
+                && ! empty($config->ssl_do_not_verify_server_cert)
             ) {
                 $options[PDO::MYSQL_ATTR_SSL_VERIFY_SERVER_CERT] = false;
             }