deletion of bootstrap cluster sometimes fails

I've noticed this in some jobs:

🗑 Delete bootstrap cluster
Cannot delete bootstrap cluster as 'pivot' Kustomization is not ready.

To delete the bootstrap cluster, you can re-run apply.sh anytime after fixing this

!3288 (merged) introduced a check that the pivot unit is ready, but I think that this check can sometimes fail if at the moment of the check the pivot unit is in status Unknown because of the periodic healthcheck.