forms: copy mobile number from user model of portail-citoyen

portail_citoyen_announces/forms.py

@@ -45,5 +45,6 @@ class SubscriptionForm(forms.Form):
         for category, transport in wanted_subscriptions:
             models.Subscription.objects.get_or_create(
                 user=self.user,
+                identifier=self.user.mobile,
                 category=category,
                 transport=transport)