add slack notification for kibana type check builds (#6174) (#6175)

(cherry picked from commit 041ec39)

Co-authored-by: margaretjgu <136839162+margaretjgu@users.noreply.github.com>

Author: github-actions[bot]

.buildkite/kibana.yml

@@ -6,3 +6,8 @@ agents:
 steps:
   - label: "Run Kibana type checks"
     command: .buildkite/kibana.sh
+
+notify:
+  - slack:
+      channels:
+        - "#devtools-notify-javascript"