twitterapi: use order constraint to force descending order

lib/pleroma/web/twitter_api/twitter_api_controller.ex

@@ -182,6 +182,7 @@ def dm_timeline(%{assigns: %{user: user}} = conn, params) do
       |> Map.put("blocking_user", user)
       |> Map.put("user", user)
       |> Map.put(:visibility, "direct")
+      |> Map.put(:order, :desc)
 
     activities =
       ActivityPub.fetch_activities_query([user.ap_id], params)