If I set run_as_user in the kubernetes section of airflow.cfg to 0, that does not get applied. The problem is this code
security_context['runAsUser'] = self.kube_config.worker_run_as_user
if self.kube_config.worker_run_as_user is an int 0, that get implied as a False and thus the security context never gets set. This also happens to fsGroup. A small change needs to be made to make this check against a "" (empty string) as that's what it's defaulted to in the default airflow config file.
Here is my pr https://github.com/apache/airflow/pull/5474