ci: scheduled workflows run on the cron lane runner

astra, heartbeat, housekeeping, sync, update and venture move to runs-on: cron
(green-tea-runner-cron), so they never queue ahead of deploys on the main runner.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VVFi3wvLWKaEkpDw6eLnQC

.github/workflows/sync.yml

@@ -20,7 +20,7 @@ concurrency:
   cancel-in-progress: false
 jobs:
   sync:
-    runs-on: ubuntu-latest
+    runs-on: cron
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@v5