[AIRFLOW-3885] Fix race condition in scheduler test (apache#4737)

We're hitting this race condition frequently now that we don't sleep()
during unit tests. We don't actually need to assert that the task is
currently running - it's fine if it has already run successfully.

tests/test_jobs.py

@@ -3249,7 +3249,7 @@ def run_with_error(task):
         executor.do_update = True
         do_schedule()
         ti.refresh_from_db()
-        self.assertEqual(ti.state, State.RUNNING)
+        self.assertIn(ti.state, [State.RUNNING, State.SUCCESS])
 
     @unittest.skipUnless("INTEGRATION" in os.environ, "Can only run end to end")
     def test_retry_handling_job(self):