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
'key': 'test-xcom-key-1',
                        'task_id': task_id_1,
                        'timestamp': "TIMESTAMP",
                    },
                    {
                        'dag_id': dag_id_1,
                        'execution_date': execution_date,
                        'key': 'test-xcom-key-2',
                        'task_id': task_id_1,
                        'timestamp': "TIMESTAMP",
                    },
                    {
                        'dag_id': dag_id_2,
                        'execution_date': execution_date,
                        'key': 'test-xcom-key-1',
                        'task_id': task_id_2,
                        'timestamp': "TIMESTAMP",
                    },
                    {
                        'dag_id': dag_id_2,
                        'execution_date': execution_date,
                        'key': 'test-xcom-key-2',
                        'task_id': task_id_2,
                        'timestamp': "TIMESTAMP",
                    },
                ],
                'total_entries': 4,
            },
        )
    def test_should_respond_200_with_tilde_and_granular_dag_access(self):