Schedule the test CI workflow monthly

Author: mdpiper

.github/workflows/test.yml

@@ -1,6 +1,10 @@
 name: Test
 
-on: [push, pull_request]
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '24 4 3 * *'  # 4:24a on third day of the month
 
 concurrency:
   group: ${{ github.ref }}-${{ github.workflow }}