Faltaba importar Q

src/eventos/views.py

@@ -25,7 +25,7 @@ from .models import Evento, Reserva, ListaEspera, Noticia
 from .forms import ListaEsperaForm, EventoForm, MensajeCorreoForm
 
 from django.contrib.auth import get_user_model
-from django.db.models import Count
+from django.db.models import Count, Q
 
 User = get_user_model()