you have to set a backoffLimit: 0 in combination with restartPolicy: Never in combination with concurrencyPolicy: Forbid.
backoffLimit means the number of times it will try before it is considered failed. The default is 6.
concurrencyPolicy set to Forbid means it will run 0 or 1 times, but not more.
restartPolicy set to Never means it won't restart on failure.
You need to do all 3 of these things, or your cronjob may run more than once.
[ADD THIS -->]backoffLimit: 0