[AIRFLOW-6979] Fix breeze test-target specific test param issue

[zhongjiajie]

Fix breeze test-target error in https://github.com/apache/airflow/blob/master/TESTING.rst#running-tests-for-a-specified-target-using-breeze-from-the-host

You can also specify individual tests or a group of tests:
./breeze test-target tests/test_core.py::TestCore

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Issue link: AIRFLOW-6979

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[zhongjiajie]

@potiuk PTAL

[potiuk]

Thanks !