Add testcases to ensure that 'soft_fail' argument is respected when running ExternalTaskSensor

[utkarsharma2]

This PR intends to add test cases to ensure that the soft_fail argument in ExternalTaskSensor is respected.

related: #34497, #33401

[hussein-awala]

No need to add this patch in the core operators, we already fixed it, and for that we add the comment (TODO: remove this if block when min_airflow_version is set to higher than 2.7.1)

However, you can keep the tests (only the tests for the execute/patch method).

[utkarsharma2]

No need to add this patch in the core operators, we already fixed it, and for that we add the comment (TODO: remove this if block when min_airflow_version is set to higher than 2.7.1)

However, you can keep the tests (only the tests for the execute/patch method).

@hussein-awala I'm assuming you mean the entire code snippet when you said this patch

# TODO: remove this if block when min_airflow_version is set to higher than 2.7.1
message = ""
if self.soft_fail:
raise AirflowSkipException(message)
raise AirflowException(message)

if so, _check_for_existence(self, session) was not respecting the soft_fail param and causing the dag.test() to halt the flow because AirflowException was raised instead of AirflowSkipException. So I'm not sure if it's handled.

or do you just mean the # TODO: remove this if block when min_airflow_version is set to higher than 2.7.1 by this patch?