Use a custom cache directory for test_stepwise tests
Use a custom cache directory for test_stepwise tests

Otherwise the tests will use tox's env cache which makes them flaky

pytest-dev/pytest,The-Compiler/pytest,txomon/pytest,The-Compiler/pytest,nicoddemus/pytest,alfredodeza/pytest,Akasurde/pytest,hackebrot/pytest,tomviner/pytest,RonnyPfannschmidt/pytest,markshao/pytest,nicoddemus/pytest,tomviner/pytest