message: add date to Zulip notification subject
diff: @@ -129,7 +129,7 @@ jobs:
  ZULIP_BOT_EMAIL: ${{ secrets.ZULIP_BOT_EMAIL }}
  ZULIP_API_TOKEN: ${{ secrets.ZULIP_API_TOKEN }}
  run: |
  - ~/.local/bin/zulip-send --stream miri --subject "Cron Job Failure" \
  + ~/.local/bin/zulip-send --stream miri --subject "Cron Job Failure $(date -uI)" \
  --message 'Dear @**RalfJ** and @**oli**
  It would appear that the Miri cron job build failed. Would you mind investigating this issue?
  