Fix tests/decorators/test_python.py for database isolation tests (#41387)

* Pass serialized parameter for dag_maker

* Serialisation of object is on __exit__ moving out the dag definition out of dag_maker context

(cherry picked from commit 278f3c4)

Author: bugraoz93

tests/decorators/test_python.py

@@ -1000,50 +1000,52 @@ def down(a: str):
 
 
 def test_teardown_trigger_rule_selective_application(dag_maker, session):
-    with dag_maker(session=session) as dag:
-
-        @dag.task
-        def my_work():
-            return "abc"
-
-        @setup
-        @dag.task
-        def my_setup():
-            return "abc"
-
-        @teardown
-        @dag.task
-        def my_teardown():
-            return "abc"
-
-        work_task = my_work()
-        setup_task = my_setup()
-        teardown_task = my_teardown()
+    with dag_maker(session=session, serialized=True) as created_dag:
+        dag = created_dag
+
+    @dag.task
+    def my_work():
+        return "abc"
+
+    @setup
+    @dag.task
+    def my_setup():
+        return "abc"
+
+    @teardown
+    @dag.task
+    def my_teardown():
+        return "abc"
+
+    work_task = my_work()
+    setup_task = my_setup()
+    teardown_task = my_teardown()
     assert work_task.operator.trigger_rule == TriggerRule.ALL_SUCCESS
     assert setup_task.operator.trigger_rule == TriggerRule.ALL_SUCCESS
     assert teardown_task.operator.trigger_rule == TriggerRule.ALL_DONE_SETUP_SUCCESS
 
 
 def test_teardown_trigger_rule_override_behavior(dag_maker, session):
-    with dag_maker(session=session) as dag:
-
-        @dag.task(trigger_rule=TriggerRule.ONE_SUCCESS)
-        def my_work():
-            return "abc"
-
-        @setup
-        @dag.task(trigger_rule=TriggerRule.ONE_SUCCESS)
-        def my_setup():
-            return "abc"
-
-        @teardown
-        @dag.task(trigger_rule=TriggerRule.ONE_SUCCESS)
-        def my_teardown():
-            return "abc"
-
-        work_task = my_work()
-        setup_task = my_setup()
-        with pytest.raises(Exception, match="Trigger rule not configurable for teardown tasks."):
-            my_teardown()
+    with dag_maker(session=session, serialized=True) as created_dag:
+        dag = created_dag
+
+    @dag.task(trigger_rule=TriggerRule.ONE_SUCCESS)
+    def my_work():
+        return "abc"
+
+    @setup
+    @dag.task(trigger_rule=TriggerRule.ONE_SUCCESS)
+    def my_setup():
+        return "abc"
+
+    @teardown
+    @dag.task(trigger_rule=TriggerRule.ONE_SUCCESS)
+    def my_teardown():
+        return "abc"
+
+    work_task = my_work()
+    setup_task = my_setup()
+    with pytest.raises(Exception, match="Trigger rule not configurable for teardown tasks."):
+        my_teardown()
     assert work_task.operator.trigger_rule == TriggerRule.ONE_SUCCESS
     assert setup_task.operator.trigger_rule == TriggerRule.ONE_SUCCESS