**Apache Airflow version**

13faa6912f7cd927737a1dc15630d3bbaf2f5d4d

**Environment**

- **Configuration**: Local Executor
- **OS** (e.g. from /etc/os-release): Mac OS 11.3
- **Kernel**: Darwin Kernel Version 20.4.0
- **Install tools**: `pip install -e .`

**The DAG**

```python
@task
def one():
    return 1

@task_group
def trivial_group(inval):

    @task
    def add_one(i):
        return i + 1

    outval = add_one(inval)
    return outval

@task
def print_it(inval):
    print(inval)

@dag(schedule_interval=None, start_date=days_ago(1), default_args={"owner": "airflow"})
def wrap():

    x = one()
    y = trivial_group(x)
    z = print_it(y)

wrap_dag = wrap()
```

**What happened**:
`print_it` had no predecessors and receives `<airflow.utils.task_group.TaskGroup object at 0x128921940>`

**What you expected to happen**:
`print_it` comes after `trivial_group.add_one` and receives `2`

The caller ends up with the task group itself, equivalent in the traditional api to `tg_ref` in:
```
with TaskGroup("trivial_group") tg_ref:
    pass
````

This interrupts the ability to continue using the Task Flow api because passing it into a function annotated with `@task` fails to register the dependency with whatever magic gets it out of xcom and adds edges to the dag.

**To Replicate**

```
 $ airflow dags test wrap $(date "+%Y-%m-%d")
```
tests/utils/test_task_group.py
task2 = DummyOperator(task_id="task2")
                task3 = DummyOperator(task_id="task3")
                task4 = DummyOperator(task_id="task4")
                task2 >> [task3, task4]
            task5 = DummyOperator(task_id="task5")
            task5 << group_b
        task1 >> group_a
        with TaskGroup("group_c") as group_c:
            task6 = DummyOperator(task_id="task6")
            task7 = DummyOperator(task_id="task7")
            task8 = DummyOperator(task_id="task8")
            [task6, task7] >> task8
            group_a >> group_c
        task5 >> task8
        task9 = DummyOperator(task_id="task9")
        task10 = DummyOperator(task_id="task10")
        group_c >> [task9, task10]
        with TaskGroup("group_d") as group_d:
            task11 = DummyOperator(task_id="task11")
            task12 = DummyOperator(task_id="task12")
            task11 >> task12
        group_d << group_c
    nodes = task_group_to_dict(dag.task_group)
    edges = dag_edges(dag)
    assert extract_node_id(nodes) == {
        'id': None,
        'children': [
            {
                'id': 'group_a',
                'children': [