support Laravel9

[s-ichikawa]

same as a title

[binaryk]

Thank you!

[Koozza]

Found a small bug. Could you change line 192 of the SendgridTransport class to:

    'type' => $this->getAttachmentContentType($attachment),

And add the following method:

    private function getAttachmentContentType(Datapart $dataPart): string
    {
        return $dataPart->getMediaType() . '/' . $dataPart->getMediaSubtype();
    }

This fixes the attachments not being readable by some mail clients!