Django Admin Staffusers - Fix duplicate user issue (#4564)

* Fix duplicate user issue

Fixes the scenario where there are 2 users of the same email in the DB (`.get` only works with one record).

* Linting

backend/users/management/commands/create_staffusers.py

@@ -90,9 +90,10 @@ def handle(self, *args, **kwargs):
                         ).save()
 
                         # attempt to update the user.
-                        try:
-                            user = User.objects.get(email=email, is_staff=True)
+                        user = User.objects.filter(email=email, is_staff=True)
 
+                        if user.exists():
+                            user = user.first()
                             user.groups.clear()
                             match role:
                                 case "readonly":
@@ -106,8 +107,7 @@ def handle(self, *args, **kwargs):
                             user.save()
                             logger.info(f"Synced {email} to a StaffUser role.")
 
-                        # for whatever reason, this failed. Revert staffuser creation.
-                        except User.DoesNotExist:
+                        else:
                             transaction.set_rollback(True)
                             logger.warning(
                                 f"StaffUser not created for {email}, they have not logged in yet."