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
return [
            XCom(
                key=f'TEST_XCOM_KEY{i}',
                execution_date=self.execution_date_parsed,
                task_id=self.task_id,
                dag_id=self.dag_id,
                timestamp=self.execution_date_parsed,
            )
            for i in range(1, count + 1)
        ]