### Apache Airflow version

Other Airflow 2 version (please specify below)

### What happened

Airflow 2.3.4 (but actual code seems to have same behaviour).

I have mapped task with xcom value.

I want to get xcom value of particular instance or xcom values of all task instances.

I am using standard REST API method /dags/{dag_id}/dagRuns/{dag_run_id}/taskInstances/{task_id}/xcomEntries/{xcom_key}

And it throws an error
`
  File &#34;/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/orm/query.py&#34;, line 2850, in one_or_none
    return self._iter().one_or_none()
  File &#34;/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/engine/result.py&#34;, line 1510, in one_or_none
    return self._only_one_row(
  File &#34;/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/engine/result.py&#34;, line 614, in _only_one_row
    raise exc.MultipleResultsFound(
sqlalchemy.exc.MultipleResultsFound: Multiple rows were found when one or none was required
`

Is it any way of getting xcom of mapped tasks via API?

### What you think should happen instead

_No response_

### How to reproduce

Make dag with mapped task. Return xcom value in every task. Try to get xcom value via API.

### Operating System

ubuntu 20.04

### Versions of Apache Airflow Providers

_No response_

### Deployment

Other

### Deployment details

Standard

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

"""Use time-machine to "stub" sleep.
    This means the ``sleep()`` takes no time, but ``datetime.now()`` appears to move forwards.
    If your module under test does ``import time`` and then ``time.sleep``:
    .. code-block:: python
        def test_something(frozen_sleep):
            my_mod.fn_under_test()
    If your module under test does ``from time import sleep`` then you will
    have to mock that sleep function directly:
    .. code-block:: python
        def test_something(frozen_sleep, monkeypatch):
            monkeypatch.setattr("my_mod.sleep", frozen_sleep)
            my_mod.fn_under_test()
    """
    traveller = None
    def fake_sleep(seconds):
        nonlocal traveller
        utcnow = datetime.utcnow()
        if traveller is not None:
            traveller.stop()
        traveller = time_machine.travel(utcnow + timedelta(seconds=seconds))
        traveller.start()
    monkeypatch.setattr("time.sleep", fake_sleep)
    yield fake_sleep
    if traveller is not None:
        traveller.stop()
@pytest.fixture(scope="session")
def app():