fix: broken upload of attachment via api

fixes an issue raised in 5cf4861 as `$data` is not required but was marked as required.

Signed-off-by: Somebodyisnobody <35230554+Somebodyisnobody@users.noreply.github.com>

Author: Somebodyisnobody

lib/Controller/AttachmentApiController.php

@@ -47,7 +47,7 @@ public function display(int $cardId, int $attachmentId, string $type = 'deck_fil
 	#[NoAdminRequired]
 	#[CORS]
 	#[NoCSRFRequired]
-	public function create(int $cardId, string $type, string $data): DataResponse {
+	public function create(int $cardId, string $type, ?string $data): DataResponse {
 		$attachment = $this->attachmentService->create($cardId, $type, $data);
 		return new DataResponse($attachment, HTTP::STATUS_OK);
 	}