fix: GetBucketCORS returns 404 if there are no policies

Similar issue @ ceph:
https://github.com/ceph/ceph/pull/27122/files
https://tracker.ceph.com/issues/38886

Implementation @ minio:
https://github.com/minio/minio/blob/de234b888c26cc191f3062a625af82640c966795/cmd/dummy-handlers.go#L196

src/api/s3/cors.rs

@@ -29,7 +29,7 @@ pub async fn handle_get_cors(ctx: ReqCtx) -> Result<Response<ResBody>, Error> {
 			.body(string_body(xml))?)
 	} else {
 		Ok(Response::builder()
-			.status(StatusCode::NO_CONTENT)
+			.status(StatusCode::NOT_FOUND)
 			.body(empty_body())?)
 	}
 }