make check-pytest: Don't pass __init__.py files to pytest
make check-pytest: Don't pass __init__.py files to pytest

It causes pytest to run some of the tests twice (and they fail the
second time because they have exhausted a generator passed as a test
fixture). This happens with pytest 6.2.5 (Ubuntu 22.04) but not pytest
4.6.9 (Ubuntu 20.04). It looks like
<https://github.com/pytest-dev/pytest/issues/9263>.

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester