[AIRFLOW-4883] Bug-fix to killing hung file processes (#5706)
[AIRFLOW-4883] Bug-fix to killing hung file processes (#5706)

PRs #5615 and #5605 and fought a bit over this change, and this is
hard (but not impossible) to test so we didn't notice.

(cherry picked from commit 3e3c0cd67272f9a400415cff7691218a80ff97aa)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow