Most python tutorials, such as
https://packaging.python.org/en/latest/tutorials/packaging-projects/#creating-a-test-directory
or https://docs.pytest.org/en/stable/explanation/goodpractices.html
recommend using "tests" folder name.

"test" is a module from the standard library, by naming the tests folder
"test", we have been shadowing the python standard library with one
of the test module, as we can see when importing "test" with the
generated python_for_test interpreter.

This was not extremely bad, but buildout integration with newer pip no
longer allow this, aligning the behavior with what using pip/venv
directly does.