reduce CCCL nightly frequency

.github/workflows/ci-workflow-nightly.yml

@@ -23,7 +23,7 @@ defaults:
 on:
   workflow_dispatch:
   schedule:
-  - cron: '0 */2 * * *'
+  - cron: '0 */4 * * *'
 
 concurrency:
   group: ${{ github.workflow }}-on-${{ github.event_name }}-from-${{ github.ref_name }}