Cyclic dependency in Python packages with PKGSRC_RUN_TEST

[Roland Illig <roland.illig%gmx.de@localhost>]

I have set up a bulk build with PKGSRC_RUN_TEST=yes. After resolving all
the dependencies, I end up with this:

Cyclic dependency for package:
py37-brotlipy-0.7.0
py37-cffi-1.14.0nb1
py37-test-5.3.5
py37-argcomplete-1.11.1
py37-flake8-3.7.9
py37-pylint-2.4.4
py37-isort-4.3.21
py37-lama-7.7.1
py37-radon-4.1.0
py37-tox-3.12.1
py37-freezegun-0.3.15
py37-dateutil-2.8.1
py37-setuptools-44.0.0
py37-paver-1.3.4
py37-virtualenv-16.7.9
py37-pypiserver-1.3.2
py37-twine-1.13.0
py37-requests-toolbelt-0.9.1
py37-betamax-0.8.1
py37-requests-2.23.0
py37-test-httpbin-1.0.0
py37-httpbin-0.7.0
py37-brotlipy-0.7.0

That's a nice large chain of cyclic dependencies. How am I supposed to
break this chain? I could manually disable the tests for one of the
packages, but which one?