Fix failing Databricks tests

[pankajkoti]

Following tests for Databricks are failing and observed in a non-related PR: #290

1. test_databricks_submit_run_operator_async
   tests/databricks/operators/test_databricks.py:59: in test_databricks_submit_run_operator_async operator.execute(context) astronomer/providers/databricks/operators/databricks.py:32: in execute context["ti"].xcom_push(key=XCOM_RUN_ID_KEY, value=self.run_id) E KeyError: 'ti'

2. test_databricks_run_now_operator_async
   tests/databricks/operators/test_databricks.py:83: in test_databricks_run_now_operator_async operator.execute(context) astronomer/providers/databricks/operators/databricks.py:86: in execute context["ti"].xcom_push(key=XCOM_RUN_ID_KEY, value=self.run_id) E TypeError: 'function' object is not subscriptable

[pankajkoti]

PR #292 merged.