Add use_spoilers property to TRIVIA_LIST_SCHEMA schema (#5566)

* Add `use_spoilers` to schema

* Update session.py

Co-authored-by: Jakub Kuczys <6032823+jack1142@users.noreply.github.com>

redbot/cogs/trivia/trivia.py

@@ -37,6 +37,7 @@ TRIVIA_LIST_SCHEMA = Schema(
             Optional("bot_plays"): bool,
             Optional("reveal_answer"): bool,
             Optional("payout_multiplier"): Or(int, float),
+            Optional("use_spoilers"): bool,
         },
         str: [str, int, bool, float],
     }