Ref: https://github.com/pytest-dev/pytest/issues/4321#issuecomment-436951894
Hardens some of the not many tests affected by this:
1. `testing/test_session.py::test_rootdir_option_arg` displayed:
> root/test_rootdir_option_arg2/test_rootdir_option_arg.py
2. `test_cmdline_python_namespace_package` displayed "hello/" prefix for:
> hello/test_hello.py::test_hello
> hello/test_hello.py::test_other