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
for i in [1, 2]:
            XCom.set(
                key=f'test-xcom-key-{i}',
                value="TEST",
                execution_date=execution_date,
                task_id=task_id,
                dag_id=dag_id,
            )
        dag = DagModel(dag_id=dag_id)
        session.add(dag)
        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 TestPaginationGetXComEntries(TestXComEndpoint):