testing/test_runner: make SetupState tests use a proper SetupState
testing/test_runner: make SetupState tests use a proper SetupState

Previously the tests (probably unintentionally) mixed a fresh SetupState
and the generated item Session's SetupState, which led to some serious
head scratching when prodding it a bit.

nicoddemus/pytest,markshao/pytest,pytest-dev/pytest,RonnyPfannschmidt/pytest,Akasurde/pytest,nicoddemus/pytest