Avoid GHA workflow being automatically stopped

Add an empty commit to the master branch once a month.

See #22

Author: k-takata

.github/workflows/trigger.yml

@@ -0,0 +1,17 @@
+name: Trigger new build
+on:
+  schedule:
+    - cron: '15 11 3 * *'
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout master
+        uses: actions/checkout@v2
+      - name: Create an empty commit and push it
+        run: |
+          git config --local user.name 'github-actions'
+          git config --local user.email '41898282+github-actions[bot]@users.noreply.github.com'
+          git commit --allow-empty -m 'Trigger a new build'
+          git push origin master