ci: Send Slack notifications when important builds fail (no-changelog) (#4638)

ci: Send Slack notifications when important builds fail

.github/workflows/test-workflows.yml

@@ -93,3 +93,11 @@ jobs:
       #     git config --global user.email 'n8n-test-bot@users.noreply.github.com'
       #     git commit -am "Automated credential update"
       #     git push --force --quiet "https://janober:${{ secrets.TOKEN }}@github.com/n8n-io/test-workflows.git" main:main
+
+      - name: Notify Slack on failure
+        uses: act10ns/slack@v2.0.0
+        if: failure()
+        with:
+          status: ${{ job.status }}
+          channel: '#updates-build-alerts'
+          webhook-url: ${{ secrets.SLACK_WEBHOOK_URL }}