fix: change import to django.conf

Signed-off-by: Guilhem Barthés <guilhem.barthes@owkin.com>

backend/users/management/commands/sync_users.py

@@ -1,4 +1,4 @@
-from django.config import settings
+from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.contrib.auth.password_validation import validate_password
 from django.core.exceptions import ValidationError