Cronjob locking not working properly

short description

If a cronjob (e.g. website backups) is taking a really long time, it gets started again even though it is still running.

Cronjobs should be locked according to running status in sys_cron.

Is caused by cronjob::run() which will reset running status through onCompleted() after the first failed attempt. Will supply MR.

Server OS: debian Server OS version: buster ISPConfig version: 3.1.0.0