MAPG-199 fix issues found by PHPStan

src/Mailing/Mail.php

@@ -77,7 +77,7 @@ class Mail
         }
     }
 
-    private function sendMail(PHPMailer $mailer, array $recipient)
+    private function sendMail(PHPMailer $mailer, array $recipient): void
     {
         $mailer->clearAddresses();
         $mailer->addAddress($recipient[0], $recipient[1]);