run CI on a nightly schedule and notify on failure

.github/workflows/cd.yml

@@ -8,7 +8,7 @@ on:
 jobs:
   deploy:
     runs-on: ubuntu-latest
-    if: ${{ github.event.workflow_run.conclusion == 'success' }}
+    if: ${{ github.event.workflow_run.conclusion == 'success' && github.event.workflow_run.event != 'schedule' }}
     steps:
       - uses: actions/checkout@v3
       - name: Tag and Push Gem

.github/workflows/ci.yml

@@ -1,6 +1,12 @@
 name: CI
 
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  schedule:
+    - cron: "0 0 * * *"
 
 jobs:
   rspec:
@@ -10,7 +16,7 @@ jobs:
         ruby:
           # See comment comes from https://github.com/ruby/setup-ruby#matrix-of-ruby-versions
           # Due to https://github.com/actions/runner/issues/849, we have to use quotes for '3.0'
-          - '3.0.6'
+          - "3.0.6"
           - 3.1
           - 3.2
           - 3.3
@@ -27,7 +33,7 @@ jobs:
       - name: Set up Ruby ${{ matrix.ruby }}
         uses: ruby/setup-ruby@v1
         with:
-          bundler-cache: false 
+          bundler-cache: false
           ruby-version: ${{ matrix.ruby }}
       - name: Update bundler
         run: gem install bundler && bundle install
@@ -45,3 +51,17 @@ jobs:
           ruby-version: head
       - name: Run static type checks
         run: bundle exec srb tc
+  notify_on_failure:
+    runs-on: ubuntu-latest
+    needs: [rspec, static_type_check]
+    if: ${{ failure() && github.ref == 'refs/heads/main' }}
+    env:
+      SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+      SLACK_WEBHOOK_TYPE: INCOMING_WEBHOOK
+    steps:
+      - uses: slackapi/[email protected]
+        with:
+          payload: |
+            {
+              "text": "${{ github.repository }}/${{ github.ref }}: FAILED\n${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}"
+            }