Mismatched Xcom Map Index when Dynamic Mapping over TaskGroup and not all mapped tasks have run

### Apache Airflow version Other Airflow 2 version (please specify below) ### If "Other Airflow 2 version" selected, which one? 2.8.3 ### What happened? If a TaskGroup is dynamically mapped, the Xcom map index for downstream tasks to pull from is mismatched. This is due to the Xcom length not being the same length as the number of mapped tasks resulting in the following error: ` File "/home/airflow/.local/lib/python3.11/site-packages/airflow/models/xcom.py", line 795, in __getitem__ raise IndexError(key) from None IndexError: 5` This is a simplified DAG that reproduces the problem. One mapped task is caused to reschedule instead of complete causing the shortened Xcom dict: ```from datetime import datetime, timedelta from airflow.decorators import task, task_group from airflow.operators.python import get_current_context from airflow import DAG from airflow.operators.empty import EmptyOperator from airflow.sensors.base import PokeReturnValue default_args = { 'owner': 'dev', 'depends_on_past': False, 'start_date': datetime(2019, 1, 1), 'provide_context': True, 'retries': 0, 'retry_delay': timedelta(seconds=30) } @task def parse_csv_schedule(): items_dict = [{'A': 1}, {'B': 2}, {'C': 3}, {'D': 4}, {'E': 5}, {'F': 6}] return items_dict @task_group(group_id="process_items") def process_items(items_dict: dict): @task.sensor(poke_interval=90, mode="reschedule") def retrieve_item(item: dict) -> PokeReturnValue: for letter, integer in item.items(): if integer == 3: print("Number is 3 - reschedule") return PokeReturnValue(is_done=False) else: print("Number is not 3 - Let's go") return PokeReturnValue(is_done=True, xcom_value=item) @task def process_item(item: dict): context = get_current_context() ti = context["ti"] map_index = ti.map_index print(f"Taskflow XCOM: {item}") xcom_dict = ti…