### 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)

)
    app.appbuilder.sm.sync_perm_for_dag(  
        "test-dag-id-1",
        access_control={"TestGranularDag": [permissions.ACTION_CAN_EDIT, permissions.ACTION_CAN_READ]},
    )
    create_user(app, username="test_no_permissions", role_name="TestNoPermissions")  
    yield app
    delete_user(app, username="test")  
    delete_user(app, username="test_no_permissions")  
class TestXComEndpoint:
    @staticmethod
    def clean_db():
        clear_db_dags()
        clear_db_runs()
        clear_db_xcom()
    @pytest.fixture(autouse=True)
    def setup_attrs(self, configured_app) -> None:
        """
        Setup For XCom endpoint TC
        """
        self.app = configured_app
        self.client = self.app.test_client()  
        
        self.clean_db()
    def teardown_method(self) -> None:
        """
        Clear Hanging XComs
        """
        self.clean_db()
class TestGetXComEntry(TestXComEndpoint):