Исправил импорт

programmer/models.py

@@ -8,6 +8,7 @@ from django.db.models.signals import post_save, post_delete
 from django.dispatch import receiver
 from django.core.cache import cache
 from .utils.email_notifications import send_callback_notification
+from django.utils.text import slugify
 
 logger = logging.getLogger(__name__)