Bug: Magento 2 checks the «.update_cronjob_status» file but never generates it so the «Cron script readiness check» will always fail on a Magento 2 upgrade (and my fix)

The file .update_cronjob_status is never generated.

Context: How is a «Cron script readiness check» implemented on a Magento 2 upgrade?

How to fix it

As a temporary solution you can disable the «Cron script readiness check» on a Magento 2 upgrade.