The XCom endpoint joins the XCom and DagRun tables. Currently, the output of the join isn't getting stored as a new `query` variable, as seen in the link to the following PR. We should add a new test to check that these tables are getting joined correctly.

https://github.com/apache/airflow/pull/10594/files/1fe1da978763c9919cee0d2c7eccd96438631993#diff-aa0c2f68c6177fb1587a6de6b5cfb28cR59


I will make these changes after #10594 
tests/api_connexion/endpoints/test_xcom_endpoint.py
XCom.set(
            key=xcom_key,
            value="TEST_VALUE",
            execution_date=execution_date,
            task_id=task_id,
            dag_id=dag_id,
        )
        dagrun = DR(
            dag_id=dag_id,
            run_id=dag_run_id,
            execution_date=execution_date,
            start_date=execution_date,
            run_type=DagRunType.MANUAL,
        )
        session.add(dagrun)
class TestGetXComEntries(TestXComEndpoint):
    def test_should_respond_200(self):
        dag_id = 'test-dag-id'
        task_id = 'test-task-id'
        execution_date = '2005-04-02T00:00:00+00:00'
        execution_date_parsed = parse_execution_date(execution_date)
        dag_run_id = DR.generate_run_id(DagRunType.MANUAL, execution_date_parsed)
        self._create_xcom_entries(dag_id, dag_run_id, execution_date_parsed, task_id)
        response = self.client.get(