Add 2026 GAMM RSE RDM Meeting

Author: jpthiele

_includes/events/2026.md

@@ -12,3 +12,4 @@
 | RSE Collaboration Workshop | 2026-09-23 - 2026-09-25 | Göttingen | [event page](https://events.hifis.net/event/3249/overview) | |
 | eScience'26 | 2026-09-28 - 2026-10-02 | Naples, Italy | [event page](https://www.escience-conference.org/2026/) | |
 | USRSE'26 | 2026-10-19 - 2026-10-21 | San Jose, CA, USA | [event page](https://us-rse.org/usrse26/) | |
+| GAMM RSE & RDM Meeting | 2026-11-23 - 2026-11-24 | Cologne, Germany | [event page](https://events.hifis.net/event/3698/) | |