Correctly deserialize dagrun_timeout field on DAGs (#8735)

We weren't deserializing this correctly (it was left as a float) but
nothing _was_ using it, and we hadn't explicitly tested it.

We already have example dags with this field, so we just need to check
for this field.

(cherry picked from commit 336aa27)

airflow/serialization/serialized_objects.py

@@ -548,7 +548,7 @@ def deserialize_dag(cls, encoded_dag):
                 k = "task_dict"
             elif k == "timezone":
                 v = cls._deserialize_timezone(v)
-            elif k in {"retry_delay", "execution_timeout"}:
+            elif k in {"dagrun_timeout"}:
                 v = cls._deserialize_timedelta(v)
             elif k.endswith("_date"):
                 v = cls._deserialize_datetime(v)

tests/serialization/test_dag_serialization.py

@@ -297,7 +297,7 @@ def validate_deserialized_dag(self, serialized_dag, dag):
             "params", "fileloc", "max_active_runs", "concurrency",
             "is_paused_upon_creation", "doc_md", "safe_dag_id", "is_subdag",
             "catchup", "description", "start_date", "end_date", "parent_dag",
-            "template_searchpath", "_access_control"
+            "template_searchpath", "_access_control", "dagrun_timeout"
         ]
 
         # fields_to_check = dag.get_serialized_fields()