MailerInterface::send does not return anything, but is stated in the docs

[dsentker]

In the chapter Creating & Sending Messages, the example shows the usage of a return object from MailerInterface::send().

/** @var Symfony\Component\Mailer\SentMessage $sentEmail */
$sentEmail = $mailer->send($email);
// $messageId = $sentEmail->getMessageId();

This is wrong, because the MailerInterface is returning void.

interface MailerInterface
{
    /**
     * @throws TransportExceptionInterface
     */
    public function send(RawMessage $message, Envelope $envelope = null): void;
}

[javiereguiluz]

Closing as fixed by #13194.