Run the cron every 15 minutes instead of every hour

.gitea/workflows/build-and-copy.yaml

@@ -2,7 +2,7 @@ name: Build and copy to prod
 on:
   push:
   schedule:
-    - cron: '@hourly'
+    - cron: '*/15 * * * *'
 jobs:
   build-and-copy:
     runs-on: ubuntu-latest