fix: fucking wired bug where the url is not displayed in plaintext

that how an e-mail looked before:
Moin,

es wurde ein neuer Useraccount erstellt.

[admin] sgsfg (2025-07-12 09:44:27.251212+00:00)
Related:

http://localhost:8000/user/9/
User anzeigen:

---

src/fellchensammlung/mail.py

@@ -44,6 +44,8 @@ def send_notification_email(notification_pk):
         plain_message = render_to_string('fellchensammlung/mail/notifications/report.txt', context)
     elif notification.notification_type == NotificationTypeChoices.NEW_USER:
         html_message = render_to_string('fellchensammlung/mail/notifications/new-user.html', context)
+        new_user_url = notification.user_related.get_full_url()
+        context["new_user_url"] = new_user_url
         plain_message = render_to_string('fellchensammlung/mail/notifications/new-user.txt', context)
     elif notification.notification_type == NotificationTypeChoices.AN_IS_TO_BE_CHECKED:
         html_message = render_to_string('fellchensammlung/mail/notifications/an-to-be-checked.html', context)

src/fellchensammlung/templates/fellchensammlung/mail/notifications/new-user.txt

@@ -4,9 +4,5 @@
 
 es wurde ein neuer Useraccount erstellt.
 
-{{ notification }}
-Related: {{ notification.user_related }}
-{{ notification.user_related.get_full_url }}
-
-User anzeigen: {{ notification.user_related.get_full_url }}
+User anzeigen: {{ new_user_url }}
 {% endblocktranslate %}{% endblock %}