**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
{'id': 'task5'},
        ],
    }
    edges = dag_edges(subdag)
    assert sorted((e["source_id"], e["target_id"]) for e in edges) == [
        ('group234.group34.downstream_join_id', 'task5'),
        ('group234.group34.task3', 'group234.group34.downstream_join_id'),
        ('group234.group34.task4', 'group234.group34.downstream_join_id'),
        ('group234.upstream_join_id', 'group234.group34.task3'),
        ('group234.upstream_join_id', 'group234.group34.task4'),
        ('task1', 'group234.upstream_join_id'),
    ]
    subdag_task_groups = subdag.task_group.get_task_group_dict()
    assert subdag_task_groups.keys() == {None, "group234", "group234.group34"}
    included_group_ids = {"group234", "group234.group34"}
    included_task_ids = {'group234.group34.task3', 'group234.group34.task4', 'task1', 'task5'}
    for task_group in subdag_task_groups.values():
        assert task_group.upstream_group_ids.issubset(included_group_ids)
        assert task_group.downstream_group_ids.issubset(included_group_ids)
        assert task_group.upstream_task_ids.issubset(included_task_ids)
        assert task_group.downstream_task_ids.issubset(included_task_ids)
    for task in subdag.task_group:
        assert task.upstream_task_ids.issubset(included_task_ids)
        assert task.downstream_task_ids.issubset(included_task_ids)
def test_dag_edges():
    execution_date = pendulum.parse("20200101")
    with DAG("test_dag_edges", start_date=execution_date) as dag:
        task1 = DummyOperator(task_id="task1")
        with TaskGroup("group_a") as group_a:
            with TaskGroup("group_b") as group_b: