Branch task does not prevent non-selected downstream tasks from running in TaskGroup (Airflow 3.2.x)

### Under which category would you file this issue? Providers ### Apache Airflow version 3.2.0 (also reproduced on 3.2.1) ### What happened and how to reproduce it? Branching inside a TaskGroup does not reliably prevent non-selected downstream tasks from running. Even when branch callable returns a specific task_id, sibling downstream tasks still get scheduled/run. In our production setup (KubernetesExecutor), this causes unnecessary pod starts and resource waste. Minimal example (TaskFlow + TaskGroup + branch): ```python from airflow.sdk import DAG, task, task_group from airflow.providers.standard.operators.empty import EmptyOperator from airflow.sdk.bases.operator import chain from pendulum import datetime with DAG( dag_id="repro_branch_taskgroup_32x", start_date=datetime(2026, 1, 1), schedule=None, catchup=False, ): @task_group(group_id="g") def g(): @task.branch(task_id="choose") def choose(): return "g.path_a" @task(task_id="path_a") def path_a(): print("A") @task(task_id="path_b") def path_b(): print("B should be skipped") end = EmptyOperator(task_id="end") c = choose() a = path_a() b = path_b() chain(c, [a, b], end) g() ``` ### What you think should happen instead? Only selected downstream branch task(s) should run. All non-selected downstream tasks should be marked skipped before execution. ### Operating System _No response_ ### Deployment Official Apache Airflow Helm Chart ### Apache Airflow Provider(s) _No response_ ### Versions of Apache Airflow Providers _No response_ ### Official Helm Chart version 1.18.0 ### Kubernetes Version v1.32.4 ### Helm Chart configuration _No response_ ### Docker Image customizations _No response_ ### Anything else? **Environment** Executor: KubernetesExecutor Python: 3.13 Deployment: Docker/Kubernetes DAG contains TaskGroup and mapped workloads in real case ### Are you willing …