Notifiers when runing airflow dags locally though tests

### Apache Airflow version 3.1.7 ### What happened and how to reproduce it? I am trying to port a Notifier to airflow 3 and ran into an issue when trying to run the code though `airflow dags test`. I reduced my dag down to ```python import logging from datetime import datetime from airflow import DAG from airflow.sdk import BaseNotifier, task class MyNotifier(BaseNotifier): log = logging.getLogger("MyNotifier") def notify(self, *args) -> None: self.log.info("Sending a really lovely message") @task def failing_task(): """This task will intentionally fail.""" raise Exception("This DAG is designed to fail!") with DAG( dag_id="bad_dag", start_date=datetime(2024, 1, 1), schedule=None, catchup=False, tags=["test", "failing"], on_failure_callback=MyNotifier(), ) as dag: fail_task = failing_task() ``` And then when I run `airflow dags test bad_dag 2025-10-03T08:00:00`, the task fails as expected, but then an error is thrown ``` [2026-04-02T21:35:01.741165Z] {dagrun.py:1453} ERROR - Callback failed for bad_dag Traceback (most recent call last): File "/Users/jhoran/Workspace/eda_astronomer/.venv/lib/python3.12/site-packages/airflow/models/dagrun.py", line 1451, in handle_dag_callback callback(context) File "/Users/jhoran/Workspace/eda_astronomer/.venv/lib/python3.12/site-packages/airflow/sdk/bases/notifier.py", line 136, in __call__ self.render_template_fields(context) File "/Users/jhoran/Workspace/eda_astronomer/.venv/lib/python3.12/site-packages/airflow/sdk/bases/notifier.py", line 92, in render_template_fields jinja_env = self.get_template_env(dag=dag) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/jhoran/Workspace/eda_astronomer/.venv/lib/python3.12/site-packages/airflow/sdk/definitions/_internal/templater.py", line 79, in get_template_env return dag.get_template_env(force_sandboxed=False) ^^^^^^^^^^^^^^^^^^^^ AttributeError: 'SerializedDAG' object has no attribute 'get_t…