CI: run build twice per day

.github/workflows/main.yml

@@ -5,7 +5,8 @@ on:
       - master
   pull_request:
   schedule:
-    - cron: "45 12/12 * * *"
+    - cron: '0 5 * * *'  # Runs at 05:00 UTC
+    - cron: '0 17 * * *' # Runs at 1:00 UTC
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}