### 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)

collect_ignore = [
    "tests/dags/subdir1/test_ignore_this.py",
    "tests/dags/test_invalid_dup_task.pyy",
    "tests/dags_corrupted/test_impersonation_custom.py",
    "tests/test_utils/perf/dags/elastic_dag.py",
]
@pytest.fixture()
def reset_environment():
    """Resets env variables."""
    init_env = os.environ.copy()
    yield
    changed_env = os.environ
    for key in changed_env:
        if key not in init_env:
            del os.environ[key]
        else:
            os.environ[key] = init_env[key]
@pytest.fixture()
def secret_key() -> str:
    """Return secret key configured."""
    from airflow.configuration import conf
    the_key = conf.get("webserver", "SECRET_KEY")
    if the_key is None:
        raise RuntimeError(
            "The secret key SHOULD be configured as `[webserver] secret_key` in the "
            "configuration/environment at this stage! "
        )
    return the_key
@pytest.fixture()
def url_safe_serializer(secret_key) -> URLSafeSerializer: