docs: fix cookies event documentation for type generation (#28139)

Co-authored-by: Samuel Attard <[email protected]>

docs/api/cookies.md

@@ -45,6 +45,8 @@ The following events are available on instances of `Cookies`:
 
 #### Event: 'changed'
 
+Returns:
+
 * `event` Event
 * `cookie` [Cookie](structures/cookie.md) - The cookie that was changed.
 * `cause` String - The cause of the change with one of the following values: