chore(pytest_sphinx): Fix assert

B011 Do not call assert False since python -O removes these calls.
Instead callers should raise AssertionError().

src/pytest_sphinx.py

@@ -422,7 +422,7 @@ def _DocTestRunner__run(self, test, compileflags, out):
                     self.report_unexpected_exception(out, test, example, exception)
                 failures += 1
             else:
-                assert False, ("unknown outcome", outcome)
+                raise AssertionError(f"unknown outcome: {outcome}")
 
             if failures and self.optionflags & doctest.FAIL_FAST:
                 break