### 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)

"""Helper that setups Airflow testing environment."""
    print(" AIRFLOW ".center(60, "="))
    
    home = os.path.expanduser("~")
    airflow_home = os.environ.get("AIRFLOW_HOME") or os.path.join(home, "airflow")
    print(f"Home of the user: {home}\nAirflow home {airflow_home}")
    
    lock_file = os.path.join(airflow_home, ".airflow_db_initialised")
    if request.config.option.db_init:
        print("Initializing the DB - forced with --with-db-init switch.")
        initial_db_init()
    elif not os.path.exists(lock_file):
        print(
            "Initializing the DB - first time after entering the container.\n"
            "You can force re-initialization the database by adding --with-db-init switch to run-tests."
        )
        initial_db_init()
        
        with open(lock_file, "w+"):
            pass
    else: