perf: Disable delete admin user

apps/users/api/user.py

@@ -4,6 +4,7 @@ from collections import defaultdict
 from django.utils.translation import gettext as _
 from rest_framework import generics
 from rest_framework.decorators import action
+from rest_framework.exceptions import PermissionDenied
 from rest_framework.response import Response
 from rest_framework_bulk import BulkModelViewSet
 
@@ -57,6 +58,11 @@ class UserViewSet(CommonApiMixin, UserQuerysetMixin, SuggestionMixin, BulkModelV
             raise UnableToDeleteAllUsers()
         return True
 
+    def perform_destroy(self, instance):
+        if instance.username == 'admin':
+            raise PermissionDenied(_("Cannot delete the admin user. Please disable it instead."))
+        super().perform_destroy(instance)
+
     @action(methods=['get'], detail=False, url_path='suggestions')
     def match(self, request, *args, **kwargs):
         with tmp_to_root_org():