pypy 3.7 CI build failing

[graingert]

pypy 3.7 fails with a core dump:

Fatal Python error: Aborted

Stack (most recent call first, approximate line numbers):
  File "<frozen importlib._bootstrap>", line 220 in _call_with_frames_removed
make: *** [Makefile:8: ci] Aborted (core dumped)

[graingert]

Looks like it's failing due to the trustme import in the nosan_server fixture