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/update.yml

@@ -12,7 +12,7 @@ permissions:
 jobs:
   update:
     if: github.repository != (vars.TIME_UPSTREAM || 'teahubxyz/time')
-    runs-on: ubuntu-latest
+    runs-on: cron
     timeout-minutes: 3
     env:
       UPSTREAM: ${{ vars.TIME_UPSTREAM || 'teahubxyz/time' }}