AddEmbeddedImageTest: switch to preSend()
AddEmbeddedImageTest: switch to preSend()

The actual "attaching" of the images happens within `createBody()` which is called from `preSend()`, so this test doesn't actually need to call `send()`.

PHPMailer/PHPMailer,PHPMailer/PHPMailer,nawawi/PHPMailer,jimjag/PHPMailer,jimjag/PHPMailer,nawawi/PHPMailer