[BUG] CI breaks with pytest v8.0.0

[willGraham01]

CI (specifically pytest) now fails in the setup phase since version 8 was released. This is likely due to the changes to the collection phase, although I haven't had time to delve into the details.

Regardless, the tests themselves are not failing - rather pytest is failing to setup the tests themselves.

Failing workflow: https://github.com/brainglobe/cellfinder/actions/runs/7740974117/job/21107107180

Pytest version 8 release notes: https://docs.pytest.org/en/latest/changelog.html

[willGraham01]

Seems we're not alone, the culprit is pytest-lazy-fixture: TvoroG/pytest-lazy-fixture#65

Since this tool hasn't seen an update in 2+ years, going to stage an update which no longer depends on it.