There should be a comma after the last array item in a multi-line array

Author: ramonjd

src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php

@@ -1342,7 +1342,7 @@ public function get_collection_params() {
 			'description' => __( 'Limit result set to attachments of a particular MIME type or MIME types.' ),
 			'type'        => 'array',
 			'items'       => array(
-				'type' => 'string'
+				'type' => 'string',
 			),
 		);