test_stepwise.py::test_fail_and_continue_with_stepwise is flaky on ubuntu-pyp3

[bluetech]

Previously: #4366, was fixed in #4382 but appears to have regressed.

Happened several times recently. Example run: https://github.com/pytest-dev/pytest/runs/583181149

2020-04-13T16:53:43.8767216Z _____________________ test_fail_and_continue_with_stepwise _____________________
2020-04-13T16:53:43.8769391Z [gw1] linux -- Python 3.6.9 /home/runner/work/pytest/pytest/.tox/pypy3-xdist/bin/python
2020-04-13T16:53:43.8769795Z 
2020-04-13T16:53:43.8771555Z stepwise_testdir = <Testdir local('/tmp/pytest-of-runner/pytest-0/popen-gw1/test_fail_and_continue_with_stepwise0')>
2020-04-13T16:53:43.8771916Z 
2020-04-13T16:53:43.8772529Z     def test_fail_and_continue_with_stepwise(stepwise_testdir):
2020-04-13T16:53:43.8773295Z         # Run the tests with a failing second test.
2020-04-13T16:53:43.8774412Z         result = stepwise_testdir.runpytest(
2020-04-13T16:53:43.8775821Z             "-v", "--strict-markers", "--stepwise", "--fail"
2020-04-13T16:53:43.8776227Z         )
2020-04-13T16:53:43.8776536Z >       assert not result.stderr.str()
2020-04-13T16:53:43.8778100Z E       assert not "Exception ignored in: <_io.FileIO name=23 mode='wb' closefd=True>\nResourceWarning: unclosed file <_io.BufferedWriter name=23>"
2020-04-13T16:53:43.8779090Z E        +  where "Exception ignored in: <_io.FileIO name=23 mode='wb' closefd=True>\nResourceWarning: unclosed file <_io.BufferedWriter name=23>" = <bound method LineMatcher.str of <_pytest.pytester.LineMatcher object at 0x000000000ab78d08>>()
2020-04-13T16:53:43.8779890Z E        +    where <bound method LineMatcher.str of <_pytest.pytester.LineMatcher object at 0x000000000ab78d08>> = <_pytest.pytester.LineMatcher object at 0x000000000ab78d08>.str
2020-04-13T16:53:43.8782193Z E        +      where <_pytest.pytester.LineMatcher object at 0x000000000ab78d08> = <RunResult ret=ExitCode.INTERRUPTED len(stdout.lines)=27 len(stderr.lines)=2 duration=0.25s>.stderr
2020-04-13T16:53:43.8782616Z 
2020-04-13T16:53:43.8783199Z /home/runner/work/pytest/pytest/testing/test_stepwise.py:91: AssertionError
2020-04-13T16:53:43.8786259Z ----------------------------- Captured stdout call -----------------------------
2020-04-13T16:53:43.8786717Z ============================= test session starts ==============================
2020-04-13T16:53:43.8787387Z platform linux -- Python 3.6.9[pypy-7.3.0-final], pytest-5.4.1.dev128+gfcfe9e6ee, py-1.8.1, pluggy-0.13.1 -- /home/runner/work/pytest/pytest/.tox/pypy3-xdist/bin/python
2020-04-13T16:53:43.8787767Z cachedir: .cache
2020-04-13T16:53:43.8788331Z rootdir: /tmp/pytest-of-runner/pytest-0/popen-gw1/test_fail_and_continue_with_stepwise0, inifile: tox.ini
2020-04-13T16:53:43.8788704Z collecting ... collected 6 items
2020-04-13T16:53:43.8788984Z stepwise: no previously failed tests, not skipping.
2020-04-13T16:53:43.8789237Z 
2020-04-13T16:53:43.8789724Z test_a.py::test_success_before_fail PASSED                               [ 16%]
2020-04-13T16:53:43.8790110Z test_a.py::test_fail_on_flag FAILED                                      [ 33%]
2020-04-13T16:53:43.8790368Z 
2020-04-13T16:53:43.8790663Z =================================== FAILURES ===================================
2020-04-13T16:53:43.8790965Z ______________________________ test_fail_on_flag _______________________________
2020-04-13T16:53:43.8791202Z 
2020-04-13T16:53:43.8791489Z request = <FixtureRequest for <Function test_fail_on_flag>>
2020-04-13T16:53:43.8791724Z 
2020-04-13T16:53:43.8792017Z     def test_fail_on_flag(request):
2020-04-13T16:53:43.8792826Z >       assert not request.config.getvalue('fail')
2020-04-13T16:53:43.8793359Z E       AssertionError: assert not True
2020-04-13T16:53:43.8794131Z E        +  where True = <bound method Config.getvalue of <_pytest.config.Config object at 0x0000000008a393d0>>('fail')
2020-04-13T16:53:43.8794533Z E        +    where <bound method Config.getvalue of <_pytest.config.Config object at 0x0000000008a393d0>> = <_pytest.config.Config object at 0x0000000008a393d0>.getvalue
2020-04-13T16:53:43.8794860Z E        +      where <_pytest.config.Config object at 0x0000000008a393d0> = <FixtureRequest for <Function test_fail_on_flag>>.config
2020-04-13T16:53:43.8795721Z 
2020-04-13T16:53:43.8796030Z test_a.py:5: AssertionError
2020-04-13T16:53:43.8796261Z =========================== short test summary info ============================
2020-04-13T16:53:43.8797465Z FAILED test_a.py::test_fail_on_flag - AssertionError: assert not True
2020-04-13T16:53:43.8797751Z !!!!!!!! Interrupted: Test failed, continuing from this test next run. !!!!!!!!!
2020-04-13T16:53:43.8798344Z ========================= 1 failed, 1 passed in 0.16s ==========================
2020-04-13T16:53:43.8799049Z ----------------------------- Captured stderr call -----------------------------
2020-04-13T16:53:43.8799524Z Exception ignored in: <_io.FileIO name=23 mode='wb' closefd=True>
2020-04-13T16:53:43.8799803Z ResourceWarning: unclosed file <_io.BufferedWriter name=23>

[bluetech]

Hasn't happened recently