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
def setUp(self):
        super().setUp()
        self.dag_id = 'test-dag-id'
        self.task_id = 'test-task-id'
        self.execution_date = '2005-04-02T00:00:00+00:00'
        self.execution_date_parsed = parse_execution_date(self.execution_date)
        self.dag_run_id = DR.generate_run_id(DagRunType.MANUAL, self.execution_date_parsed)
    @parameterized.expand(
        [
            (
                "limit=1",
                ["TEST_XCOM_KEY1"],
            ),
            (
                "limit=2",
                ["TEST_XCOM_KEY1", "TEST_XCOM_KEY10"],
            ),
            (
                "offset=5",
                [
                    "TEST_XCOM_KEY5",
                    "TEST_XCOM_KEY6",
                    "TEST_XCOM_KEY7",
                    "TEST_XCOM_KEY8",
                    "TEST_XCOM_KEY9",
                ],
            ),
            (