Merge pull request #6639 from flatcar-linux/t-lo/slack-add-flatcar

slack config: add Flatcar channel

Author: k8s-ci-robot

communication/slack-config/channels.yaml

@@ -104,6 +104,7 @@ channels:
   - name: falco
   - name: fiaas
   - name: fi-users
+  - name: flatcar
   - name: flink-operator
   - name: fr-events
   - name: fr-users