Do not allow currency codes that to not represent money (#4056)

* Do not allow currency codes that to not represent money

* Rebase migration

* Fix blacklist

src/pretix/base/migrations/0263_auto_20240409_0732.py

@@ -0,0 +1,26 @@
+# Generated by Django 4.2.10 on 2024-04-09 07:32
+
+from django.db import migrations
+
+
+def change_currencies(apps, schema_editor):
+    Event = apps.get_model("pretixbase", "Event")
+    Event.objects.filter(
+        currency__in={
+            'XAG', 'XAU', 'XBA', 'XBB', 'XBC', 'XBD', 'XDR', 'XPD', 'XPT', 'XSU', 'XTS', 'XUA',
+        }
+    ).update(currency='XXX')
+
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("pretixbase", "0262_subevent_comment"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            change_currencies, migrations.RunPython.noop
+        )
+    ]