Add "security concerns" topic to Nov WG (#281)

Author: benjie

working-group/agendas/2023/2023-11-23.md

@@ -113,3 +113,4 @@ Benjie Gillam           | @Benjie                | Graphile                | Cha
 1. Review previous meeting's action items (5m, Organizer)
 1. [Other keys are reserved](https://github.com/graphql/graphql-over-http/pull/278) (10m, Benjie)
 1. [Advancing the spec to stage 2](https://github.com/graphql/graphql-over-http/pull/275) (5m, Benjie)
+1. [Adding a section on security concerns](https://github.com/graphql/graphql-over-http/issues/280) (30m, Benjie)