Fix #2015 -- Shift operation into a later migration

src/pretix/base/migrations/0179_auto_20210311_1653.py

@@ -47,8 +47,4 @@ class Migration(migrations.Migration):
             clean_duplicates,
             migrations.RunPython.noop,
         ),
-        migrations.AlterUniqueTogether(
-            name='questionanswer',
-            unique_together={('orderposition', 'question'), ('cartposition', 'question')},
-        ),
     ]

src/pretix/base/migrations/0180_auto_20210324_1309.py

@@ -10,6 +10,10 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
+        migrations.AlterUniqueTogether(
+            name='questionanswer',
+            unique_together={('orderposition', 'question'), ('cartposition', 'question')},
+        ),
         migrations.RemoveField(
             model_name='quota',
             name='cached_availability_number',