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
"offset=0",
                [
                    "TEST_XCOM_KEY1",
                    "TEST_XCOM_KEY10",
                    "TEST_XCOM_KEY2",
                    "TEST_XCOM_KEY3",
                    "TEST_XCOM_KEY4",
                    "TEST_XCOM_KEY5",
                    "TEST_XCOM_KEY6",
                    "TEST_XCOM_KEY7",
                    "TEST_XCOM_KEY8",
                    "TEST_XCOM_KEY9",
                ],
            ),
            (
                "limit=1&offset=5",
                ["TEST_XCOM_KEY5"],
            ),
            (
                "limit=1&offset=1",
                ["TEST_XCOM_KEY10"],
            ),
            (
                "limit=2&offset=2",
                ["TEST_XCOM_KEY2", "TEST_XCOM_KEY3"],
            ),
        ]
    )
    @provide_session
    def test_handle_limit_offset(self, query_params, expected_xcom_ids, session):