[AIRFLOW-6642] Make local task job test less flaky (#7262)
[AIRFLOW-6642] Make local task job test less flaky (#7262)

The heartbeat failed fast test is flaky - sometimes the time needed to run the
test is longer than expected.

(cherry picked from commit 8936180afb9395cbf4af2ae885136caee8b2e3b7)

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