**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)


"""
    Class that represents edge information to be added between two
    tasks/operators. Has shorthand factory functions, like Label("hooray").
    Current implementation supports
        t1 >> Label("Success route") >> t2
        t2 << Label("Success route") << t2
    Note that due to the potential for use in either direction, this waits
    to make the actual connection between both sides until both are declared,
    and will do so progressively if multiple ups/downs are added.
    This and EdgeInfo are related - an EdgeModifier is the Python object you
    use to add information to (potentially multiple) edges, and EdgeInfo
    is the representation of the information for one specific edge.
    """
    def __init__(self, label: str | None = None):
        self.label = label
        self._upstream: list[BaseOperator] = []
        self._downstream: list[BaseOperator] = []
    @property
    def roots(self):
        return self._downstream
    @property
    def leaves(self):