Fixed wrong ModelChoiceField queryset in voucher form

src/pretix/control/forms/vouchers.py

@@ -10,5 +10,9 @@ class VoucherForm(I18nModelForm):
             'code', 'valid_until', 'block_quota', 'allow_ignore_quota', 'price', 'item'
         ]
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.fields['item'].queryset = self.instance.event.items.all()
+
     def _get_validation_exclusions(self):
         return []