Use update_fields more consistently when modifying model objects.

(imported from commit a3f0c308b621b5ff85c55654f187e25749192b19)

zephyr/management/commands/dump_pointers.py

@@ -36,7 +36,7 @@ def restore(change):
                 continue
         if change:
             u.pointer = pointer
-            u.save()
+            u.save(update_fields=["pointer"])
 
 class Command(BaseCommand):
     option_list = BaseCommand.option_list + (