test__xxsubinterpreters prevents to get results from Gentoo Refleaks 3.x and Windows Refleaks 3.x, it also broke multiple CIs and it introduced random failures. For all these reasons, I skipped the test. See the general policy for CIs:
https://mail.python.org/pipermail/python-dev/2018-May/153753.html

Eric: if you need CIs to check if a change fix test__xxsubinterpreters, they are ways to trigger custom builds, but I don't recall how to do that :-D You should be able to do that on buildbots at least, the devguide explains how to do it, or ask maybe Zachary Ware. Until the crash is fixed, I would prefer to leave the test skipped.