Missing alt-text pixel in tracking image conflicts in mail-tester.com

[Rommert]

Describe the bug

Maybe not a deal breaker. The test report from mail-tester.com shows a message about a 'missing alt-text' of the tracking image.

alt="" is the most appropriate approach in this case - this tells the screenreader that the image is purely decorative and should be ignored. Since tracking pixels do not visually convey information, they are essentially decorative from this point of view. What do you think, @bencroker ?

      $htmlBody .= '<img src="'.$trackingImageUrl.'" width="1" height="1" alt="" />';

[bencroker]

Thanks, added in 9d45d1f for the next release.