LGTM.com - false positive - Python: unreachable statement in a test following with pytest.raises()

**Description of the false positive**

An "Unreachable statement." error is raised for a line in a Python test following a context manager `with pytest.raises()`. I have confirmed that the lines are indeed reachable and are executed during a test run.

**URL to the alert on the project page on LGTM.com**

https://lgtm.com/projects/g/pantsbuild/pants/snapshot/bd4b81284ec21bab9d40afae262b9bbd1e0a9501/files/src/python/pants/backend/python/target_types_test.py?sort=name&dir=ASC&mode=heatmap#xc0ed6860b3ae7315:1