Use |to_json for matrix_mautrix_discord_bridge_restricted_rooms

roles/matrix-bridge-mautrix-discord/templates/config.yaml.j2

@@ -101,7 +101,7 @@ bridge:
     message_error_notices: true
     # Should the bridge use space-restricted join rules instead of invite-only for guild rooms?
     # This can avoid unnecessary invite events in guild rooms when members are synced in.
-    restricted_rooms: {{ matrix_mautrix_discord_bridge_restricted_rooms }}
+    restricted_rooms: {{ matrix_mautrix_discord_bridge_restricted_rooms|to_json }}
     # Should the bridge update the m.direct account data event when double puppeting is enabled.
     # Note that updating the m.direct event is not atomic (except with mautrix-asmux)
     # and is therefore prone to race conditions.