Use NullTransport to not send out emails

Co-authored-by: Sam Mousa <[email protected]>

Author: mikk150

src/Codeception/Lib/Connector/Yii2.php

@@ -430,6 +430,7 @@ protected function mockMailer(array $config): array
             },
             'mailer' => [
                 'class' => Mailer::class,
+                'transportFactory' => new NullTransportFactory()
             ]
         ];