Update Pytest to v9.0.2

[rmccar]

What is the context of this PR?

Updates Pytest to v9.0.2.

This includes fixing some breaking changes including:

• When running in CI an env var now needs to be set to put it into CI mode whereas before this was default
• The warning that adding markers to fixtures will not be valid in v9 now causes an error so these now have been removed
• Subtests now work differently because the pytest-subtests plugin has been archived and that functionality has been moved into pytest itself. While this change is backwards compatible the passing of the post/get method in this way now no longer seems to work as expected so in these cases I have split those tests out.

How to review

• Run tests locally to make sure they pass
• Check that changes make sense and consistent with breaking changes needing to be fixed

Checklist

• New static content marked up for translation
• Newly defined schema content included in eq-translations repo