♻️(backend) document list order by updated_at desc

Document list is now ordered by updated_at in
descending order.
Test cases were improved as well.

src/backend/core/api/viewsets.py

@@ -310,6 +310,7 @@ class DocumentViewSet(
     access_model_class = models.DocumentAccess
     resource_field_name = "document"
     queryset = models.Document.objects.all()
+    ordering = ["-updated_at"]
 
     def perform_create(self, serializer):
         """