Upgrade to Django 4.2

[Minnozz]

• [x] Upgrade to Django 4.0
  • [x] Remove deprecated USE_L10N setting
  • [x] Use built-in support for Redis cache backend
  • [x] Move from deprecated pytz to zoneinfo
  • [x] CSRF protection now checks the Origin header; changes to CSRF_TRUSTED_ORIGINS are needed
• [x] Upgrade to Django 4.1
  • [x] Standardize order of operations in overridden save() methods due to changes in releations for unsaved model instances
• [x] Upgrade to Django 4.2
  • [x] Use new STORAGES setting
  • [x] Use new headers kwarg for test HTTP client
  • [x] Modifying update_fields in overridden save() when extra fields are modified may now be required
  • [x] Replace deprecated CICharField with custom case-insensitive collation
• [x] Group indirect dependencies in requirements.txt and change to >= (for security fixes)
• [x] Update other dependencies to the newest possible version

Other points of note:

• You can now use makemigrations --update while working on a migration
• psycopg3 is now supported; I didn't immediately upgrade because of a direct import inside a migration

[Minnozz]

Rebased on #3350 to allow defining CSRF_TRUSTED_ORIGINS correctly

[Minnozz]

@bookwyrm-social/code-review This PR is ready for review