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
(permissions.ACTION_CAN_READ, permissions.RESOURCE_XCOM),
            ],
        )
        cls.app.appbuilder.sm.sync_perm_for_dag(  
            "test-dag-id-1",
            access_control={'TestGranularDag': [permissions.ACTION_CAN_EDIT, permissions.ACTION_CAN_READ]},
        )
        create_user(cls.app, username="test_no_permissions", role_name="TestNoPermissions")  
    @classmethod
    def tearDownClass(cls) -> None:
        delete_user(cls.app, username="test")  
        delete_user(cls.app, username="test_no_permissions")  
    @staticmethod
    def clean_db():
        clear_db_dags()
        clear_db_runs()
        clear_db_xcom()
    def setUp(self) -> None:
        """
        Setup For XCom endpoint TC
        """
        self.client = self.app.test_client()  
        
        self.clean_db()
    def tearDown(self) -> None:
        """
        Clear Hanging XComs
        """
        self.clean_db()
class TestGetXComEntry(TestXComEndpoint):