Upgrade pytest-plone to version 1.1.0

[ericof]

Summary

Upgrade pytest-plone to version 1.1.0 and adopt its new create_site / app_class fixtures in the backend test suite.

Changes

• Bump pytest-plone from >=1.0.0 to >=1.1.0 in backend/pyproject.toml (and backend/uv.lock).
• Drop the locally-defined create_site fixture from backend/tests/conftest.py — it now ships with pytest-plone.
• Use the new app_class fixture instead of aq_parent(portal_class) boilerplate in tests/content_types/test_ct_lrf.py and tests/creation/conftest.py.

Testing

• uv run pytest tests/creation tests/content_types/test_ct_lrf.py → 57 passed.

Issue

Refs kitconcept/distribution-kitconcept-website#74

Local Results

x4.6 improvement:

• pytest-plone 1.0.0: 108 passed in 132.91s (0:02:12)
• pytest-plone 1.1.0: 108 passed in 28.88s