EmailAction incorrectly uses the result of $this->mailManager->mail()

Problem/Motivation

In \Drupal\action\Plugin\Action\EmailAction it does the following:

    if ($this->mailManager->mail('system', 'action_send_email', $recipient, $langcode, $params)) {
      $this->logger->notice('Sent email to %recipient', ['%recipient' => $recipient]);
    }
    else {
      $this->logger->error('Unable to send email to %recipient', ['%recipient' => $recipient]);
    }

whereas the docs from \Drupal\Core\Mail\MailManagerInterface::mail() are:

   * @return array
   *   The $message array structure containing all details of the message. If
   *   already sent ($send = TRUE), then the 'result' element will contain the
   *   success indicator of the email, failure being already written to the
   *   watchdog. (Success means nothing more than the message being accepted at
   *   php-level, which still doesn't guarantee it to be delivered.)

Proposed resolution

Remove the error logging as this is already handled and only log a notice if successful. In a way it is a shame that the success logging is not also handled by MailManager - so we have consistent logging of all email sending but that feels like a Drupal 9 type change.

Remaining tasks

User interface changes

None

API changes

None

Data model changes

None