### 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)

want_serialized = False
    
    
    serialized_marker = request.node.get_closest_marker("need_serialized_dag")
    if serialized_marker:
        (want_serialized,) = serialized_marker.args or (True,)
    from airflow.utils.log.logging_mixin import LoggingMixin
    class DagFactory(LoggingMixin):
        _own_session = False
        def __init__(self):
            from airflow.models import DagBag
            
            self.dagbag = DagBag(os.devnull, include_examples=False, read_dags_from_db=False)
        def __enter__(self):
            self.dag.__enter__()
            if self.want_serialized:
                return lazy_object_proxy.Proxy(self._serialized_dag)
            return self.dag
        def _serialized_dag(self):
            return self.serialized_model.dag
        def get_serialized_data(self):
            try:
                data = self.serialized_model.data
            except AttributeError:
                raise RuntimeError("DAG serialization not requested")
            if isinstance(data, str):
                return json.loads(data)
            return data
        def __exit__(self, type, value, traceback):