Add Matt Mahoney to Dec 2023 Primary

Author: mjmahone

agendas/2023/12-Dec/07-wg-primary.md

@@ -104,6 +104,7 @@ hold additional secondary meetings later in the month.
 | :--------------- | :------------ | :----------------- | :-------------------- |
 | Lee Byron (Host) | @leebyron     | GraphQL Foundation | San Francisco, CA, US |
 | Benjie Gillam    | @benjie       | Graphile           | Chandler's Ford, UK   |
+| Matt Mahoney     | @mjmahone     | Meta               | New York, NY, US      |
 
 ## Agenda