Fix read/unread multiple endpoints not returning ids as strings

lib/frenzy_web/controllers/fervor/items_controller.ex

@@ -101,7 +101,7 @@ defmodule FrenzyWeb.Fervor.ItemsController do
         changeset = Item.changeset(item, changes)
 
         case Repo.update(changeset) do
-          {:ok, item} -> item.id
+          {:ok, item} -> to_string(item.id)
           _ -> nil
         end
       end)