[11.x] Add support for mime types in Resend mail transport (#52006)

* feat: Add support for mime types

* Update ResendTransport.php

---------

Co-authored-by: Taylor Otwell <[email protected]>

Author: jayanratna

src/Illuminate/Mail/Transport/ResendTransport.php

@@ -75,6 +75,7 @@ protected function doSend(SentMessage $message): void
                 $filename = $headers->getHeaderParameter('Content-Disposition', 'filename');
 
                 $item = [
+                    'content_type' => $headers->get('Content-Type')->getBody(),
                     'content' => str_replace("\r\n", '', $attachment->bodyToString()),
                     'filename' => $filename,
                 ];