set executor.job_id to BackfillJob.id for backfills (#27020)

Co-authored-by: Ryan Hatter <ryan.hatter@astronomer.io>

airflow/jobs/backfill_job.py

@@ -833,7 +833,7 @@ def _execute(self, session=None):
             pickle_id = pickle.id
 
         executor = self.executor
-        executor.job_id = "backfill"
+        executor.job_id = self.id
         executor.start()
 
         ti_status.total_runs = len(dagrun_infos)  # total dag runs in backfill

tests/jobs/test_backfill_job.py

@@ -1609,8 +1609,8 @@ def test_job_id_is_assigned_to_dag_run(self, dag_maker):
         dr: DagRun = dag.get_last_dagrun()
         assert dr.creating_job_id == job.id
 
-    def test_backfill_has_job_id(self):
-        """Make sure that backfill jobs are assigned job_ids."""
+    def test_backfill_has_job_id_int(self):
+        """Make sure that backfill jobs are assigned job_ids and that the job_id is an int."""
         dag = self.dagbag.get_dag("test_start_date_scheduling")
         dag.clear()
 
@@ -1624,7 +1624,7 @@ def test_backfill_has_job_id(self):
             run_backwards=True,
         )
         job.run()
-        assert executor.job_id is not None
+        assert isinstance(executor.job_id, int)
 
     @pytest.mark.long_running
     @pytest.mark.parametrize("executor_name", ["SequentialExecutor", "DebugExecutor"])