test suite fails with some versions of pytest

[anthrotype]

I first noticed this in #3457 (comment)

Looks like pytest have just yanked a release 8.1.0 from PyPI. Our tests were passing with it, but now an older pytest 8.0.2 is being > installed and the tests suddenly fail:
pytest-dev/pytest#12069

I attempted to install a few pytest versions and it consistently fails with 8.0.1 and 8.0.2 (the latter is the latest currently available on PyPI as of 4 March 15:50 GMT).

It passes with pytest 8.1.0 released yesterday however they have decided to "yank" it from PyPI for whatever reason which I don't fully understand, so we know get 8.0.2 which fails for us.

If I pin it to ==8.0.0 it works. I have no idea what's going on.