**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)


"""Called for Task >> [Task] because list don't have __rshift__ operators."""
        self.__lshift__(other)
        return self
    def __rlshift__(self, other: DependencyMixin | Sequence[DependencyMixin]):
        """Called for Task << [Task] because list don't have __lshift__ operators."""
        self.__rshift__(other)
        return self
class TaskMixin(DependencyMixin):
    """:meta private:"""
    def __init_subclass__(cls) -> None:
        warnings.warn(
            f"TaskMixin has been renamed to DependencyMixin, please update {cls.__name__}",
            category=RemovedInAirflow3Warning,
            stacklevel=2,
        )
        return super().__init_subclass__()
class DAGNode(DependencyMixin, metaclass=ABCMeta):
    """
    A base class for a node in the graph of a workflow -- an Operator or a Task Group, either mapped or
    unmapped.
    """
    dag: DAG | None = None
    task_group: TaskGroup | None = None
    """The task_group that contains this node"""
    @property
    @abstractmethod
    def node_id(self) -> str: