chore: add a test workflow

.github/workflows/slack-test.yml

@@ -0,0 +1,33 @@
+name: slack-test
+
+on:
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Intentionally failing step
+        run: exit 123
+
+      - name: Notify about failures
+        if: failure()
+        uses: slackapi/slack-github-action@v1
+        with:
+          payload: |
+            {
+              "text": "",
+              "blocks": [
+                {
+                  "type": "section",
+                  "text": {
+                    "type": "mrkdwn",
+                    "text": "Workflow "${{ github.workflow }}" failed: https://github.com/${{ github.repository_owner }}/${{ github.repository}}/actions/runs/${{ github.run_id }})"
+                  }
+                }
+              ]
+            }
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+          SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK