**Apache Airflow version**: 2.1.0

**What happened**:

Using a Label infront of a TaskGroup breaks task dependencies, as tasks before the TaskGroup will now point to the last task in the TaskGroup.

**What you expected to happen**:

Task dependencies with or without Labels should be the same (and preferably the Label should be visible outside of the TaskGroup).
Behavior without a Label is as follows:

```python
with TaskGroup("tg1", tooltip="Tasks related to task group") as tg1:
        DummyOperator(task_id="b") >> DummyOperator(task_id="c")

DummyOperator(task_id="a") >> tg1
```
![without Taskgroup](https://user-images.githubusercontent.com/35238779/128502690-58b31577-91d7-4b5c-b348-4779c9286958.png)

**How to reproduce it**:

```python
with TaskGroup("tg1", tooltip="Tasks related to task group") as tg1:
        DummyOperator(task_id="b") >> DummyOperator(task_id="c")

    DummyOperator(task_id="a") >> Label("testlabel") >> tg1
```
![with TaskGroup](https://user-images.githubusercontent.com/35238779/128502758-5252b7e7-7c30-424a-ac3a-3f9a99b0a805.png)


#
#
from __future__ import annotations
from datetime import datetime, timedelta
import pytest
from airflow import DAG
from airflow.models.xcom_arg import XComArg
from airflow.operators.python import PythonOperator
from airflow.utils.edgemodifier import Label
from airflow.utils.task_group import TaskGroup
DEFAULT_ARGS = {
    "owner": "test",
    "depends_on_past": True,
    "start_date": datetime.today(),
    "retries": 1,
    "retry_delay": timedelta(minutes=1),
}
@pytest.fixture
def test_dag():