Fix timezone issue

shiftregister/app/models.py

@@ -4,6 +4,7 @@ from django.shortcuts import reverse
 from datetime import timedelta
 from django.utils import timezone
 from django.db.models import F, Count, Q, ExpressionWrapper, Case, When
+from django.template import Context, Template
 from phonenumber_field.modelfields import PhoneNumberField
 from dynamic_preferences.registries import global_preferences_registry
 
@@ -137,7 +138,10 @@ class ShiftRegistration(models.Model):
 
     def send_reminder(self):
         url = reverse("shift", kwargs={"shiftid": self.shift.pk})
-        text = f"Deine kontakt-Schicht beginnt um {self.shift.start_at.strftime('%H:%M')}, bitte komm 15 Minuten vorher an den Treffpunkt. https://kontakt.rocks{url}"
+        template = Template(
+            'Deine kontakt-Schicht beginnt um {{ start_at|date:"H:i" }}, bitte komm 15 Minuten vorher an den Treffpunkt. https://kontakt.rocks{{ url }}'
+        )
+        text = template.render(Context({"start_at": self.shift.start_at, "url": url}))
         msg = Message(to=self.helper, text=text)
         msg.save()
         self.reminder_sent = True