MDL-78146 lib: Added missing class properties in phpmailer

In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.

lib/phpmailer/moodle_phpmailer.php

@@ -47,7 +47,6 @@ class moodle_phpmailer extends \PHPMailer\PHPMailer\PHPMailer {
      */
     public function __construct(){
         global $CFG;
-        $this->Version   = 'Moodle '.$CFG->version;         // mailer version
         $this->CharSet   = 'UTF-8';
         // MDL-52637: Disable the automatic TLS encryption added in v5.2.10 (9da56fc1328a72aa124b35b738966315c41ef5c6).
         $this->SMTPAutoTLS = false;