**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)


"""TaskGroup context is used to keep the current TaskGroup when TaskGroup is used as ContextManager."""
    _context_managed_task_group: TaskGroup | None = None
    _previous_context_managed_task_groups: list[TaskGroup] = []
    @classmethod
    def push_context_managed_task_group(cls, task_group: TaskGroup):
        """Push a TaskGroup into the list of managed TaskGroups."""
        if cls._context_managed_task_group:
            cls._previous_context_managed_task_groups.append(cls._context_managed_task_group)
        cls._context_managed_task_group = task_group
    @classmethod
    def pop_context_managed_task_group(cls) -> TaskGroup | None:
        """Pops the last TaskGroup from the list of manged TaskGroups and update the current TaskGroup."""
        old_task_group = cls._context_managed_task_group
        if cls._previous_context_managed_task_groups:
            cls._context_managed_task_group = cls._previous_context_managed_task_groups.pop()
        else:
            cls._context_managed_task_group = None
        return old_task_group
    @classmethod
    def get_current_task_group(cls, dag: DAG | None) -> TaskGroup | None:
        """Get the current TaskGroup."""
        from airflow.models.dag import DagContext
        if not cls._context_managed_task_group:
            dag = dag or DagContext.get_current_dag()
            if dag:
                
                return dag.task_group
        return cls._context_managed_task_group
def task_group_to_dict(task_item_or_group):
    """