Revert "Debug bf860a29a3d2bb25900fc36c6888f3a833830575. Replace"

As this change breaks 1.9 build: https://screenshot.googleplex.com/Q2L1sUCzQb4
(missing timezone module import).
This reverts commit 811e261de26350852b5394bfe5a653ebf07b6cfc.

Change-Id: Id505d8e154e7fd47ad533b3e3009bdfbd4750c36
GitOrigin-RevId: 55d9502405de7512f8b7044af92951639ea59532

airflow/models.py

@@ -4406,7 +4406,7 @@ def get_state(self):
     def set_state(self, state):
         if self._state != state:
             self._state = state
-            self.end_date = func.now() if self._state in State.finished() else None
+            self.end_date = timezone.utcnow() if self._state in State.finished() else None
 
             if self.dag_id is not None:
                 # something really weird goes on here: if you try to close the session