UnboundLocalError on TriggerDagRunOperator triggering a dag that doesn't exist

### Apache Airflow version main (development) ### If "Other Airflow 3 version" selected, which one? _No response_ ### What happened? When TriggerDagRunOperator operator raises `DagRunTriggerException` in task-sdk it's handled to trigger the dag but when the target dag is invalid then API server returns 404 which is re-raised. Since the Exception is raised under a block that handles the DagRunTriggerException state variable is not set with a value causing finally block to give UnboundLocalError. When TriggerDagRunOperator tries to rerun a dag with same run_id then the conflict status code response from API server is handled. 404 can also be handled in similar manner but this feels like not something limited to TriggerDagRunOperator but in turn could be caused by others too. The other approach would be to initialize state with a sentinel value to emit stats only when it's defined. _handle_trigger_dag_run raising a ServerResponseError https://github.com/apache/airflow/blob/fabc5c35da0219f904817e54ee4393f1ae07b101/task-sdk/src/airflow/sdk/execution_time/task_runner.py#L1265-L1266 finally block accessing state that is not initialized https://github.com/apache/airflow/blob/fabc5c35da0219f904817e54ee4393f1ae07b101/task-sdk/src/airflow/sdk/execution_time/task_runner.py#L1323-L1329 ``` ::group::Log message source details sources=["/home/karthikeyan/airflow/logs/dag_id=test_non_existent_triggerdagrun/run_id=manual__2026-03-07T17:50:19.584252+00:00/task_id=trigger_dag/attempt=4.log"] ::endgroup:: [2026-03-07T18:05:25.663612Z] INFO - DAG bundles loaded: dags-folder-1, example_dags [2026-03-07T18:05:25.664236Z] INFO - Filling up the DagBag from /home/karthikeyan/airflow/dags/non_existent_dagrun.py [2026-03-07T18:05:25.717248Z] INFO - Task instance is in running state [2026-03-07T18:05:25.717448Z] INFO - Previous state of the Task instance: TaskInstanceState.QUEUED [2026-03-07T18:05:25.717663Z] INFO - Current task name:trigger_dag [2026-03-07T18:05:25.717759Z] INFO - Dag name:t…