Since the pytest pin was removed, CI installs pytest 9 on any build
running Python 3.10 or higher (pytest 9 dropped support for older
Python versions). Those builds were failing every test that made an
HTTP request, while the Python 3.8 and 3.9 builds on pytest 8 passed.

pytest 9 reworked fixture precedence and ordering. Our session-scoped
autouse `setup_siteconfig` fixture used to run before `django_db_setup`,
but under pytest 9 that order is reversed. This ended up storing
incorrect `MEDIA_ROOT` and `STATIC_ROOT` in the database, causing
several tests to fail because we were serving the
manual-updates-required page instead of intended content.

This makes `django_db_setup` depend on `setup_siteconfig` explicitly, so
the paths are always configured before the siteconfig is created. That
no longer relies on autouse fixtures being ordered first.

Testing Done:
Reproduced the fixture ordering change in isolation. pytest 8.3.5 runs
`setup_siteconfig` first, pytest 9.1.1 runs `django_db_setup` first, and
with this change both run in the correct order.

Forced the pytest 9 ordering under pytest 8 to confirm the cause. That
reproduced the CI failures, with the same manual updates templates being
rendered.

Reviewed at https://reviews.reviewboard.org/r/15228/