add hmc to slack channel (#7973)

* add hmc to channels

* rename hmc to hmc-dev

Co-authored-by: Bob Killen <[email protected]>

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Co-authored-by: Bob Killen <[email protected]>

Author: Schnitzel

communication/slack-config/channels.yaml

@@ -171,6 +171,7 @@ channels:
   - name: hephy-users
     id: C678BMZ89
   - name: hetzner
+  - name: hmc-dev
   - name: homelab
   - name: hydrophone
   - name: id-events