Limit pytest in dev requirements

[Jacob-Stevens-Haas]

See TvoroG/pytest-lazy-fixture#65 as noticed in any CI runs since pytest 8.0 was released a few weeks ago.

We often want to parametrize a test, where one value the parameter could take is a fixture. That's what pytest-lazy-fixture does.

pytest-lazy-fixture may be abandoned, so 🤷‍♂️ it might get included in pytest itself, or it might get a new maintainer, or someone may fork it and upload it as a new PyPI package. In the interim, I will limit the version of pytest in this repo.

For status of equivalent functionality in core pytest, see pytest-dev/pytest#11532