Do not use redis cache at import time (#6321)

During our [2026-06-27 incident](https://pretix.eu/about/en/blog/20260630-pretix-hosted-outage/),
we noticed that pretix is using redis at import time. This means that
gunicorn and celery process were unable to start on servers who could
currently not reach redis. This is kinda mitigated through auto-restart
on systemd or docker level, but that's not really how it is supposed to
work. Celery even has smart retry/reconnect logic that becomes pointless
this way.

src/pretix/base/forms/questions.py

@@ -53,6 +53,7 @@ from django.db.models import QuerySet
 from django.forms import Select, widgets
 from django.forms.widgets import FILE_INPUT_CONTRADICTION
 from django.utils.formats import date_format
+from django.utils.functional import lazy
 from django.utils.html import escape
 from django.utils.safestring import mark_safe
 from django.utils.text import format_lazy
@@ -324,16 +325,21 @@ class WrappedPhonePrefixSelect(Select):
     initial = None
 
     def __init__(self, initial=None):
-        choices = [("", "---------")]
+        def _get_choices():
+            choices = [("", "---------")]
+
+            if initial:
+                for prefix, values in COUNTRY_CODE_TO_REGION_CODE.items():
+                    if all(v == REGION_CODE_FOR_NON_GEO_ENTITY for v in values):
+                        continue
+                    if initial in values:
+                        self.initial = "+%d" % prefix
+                        break
+            choices += get_phone_prefixes_sorted_and_localized()
+            return choices
+
+        choices = lazy(_get_choices, list)()
 
-        if initial:
-            for prefix, values in COUNTRY_CODE_TO_REGION_CODE.items():
-                if all(v == REGION_CODE_FOR_NON_GEO_ENTITY for v in values):
-                    continue
-                if initial in values:
-                    self.initial = "+%d" % prefix
-                    break
-        choices += get_phone_prefixes_sorted_and_localized()
         super().__init__(choices=choices, attrs={
             'aria-label': pgettext_lazy('phonenumber', 'International area code'),
             'autocomplete': 'tel-country-code',