Upgrade to Django 3.2 (#2056)

src/pretix/helpers/models.py

@@ -21,6 +21,7 @@
 #
 import copy
 
+from django.core.files import File
 from django.db import models
 
 
@@ -37,7 +38,7 @@ def modelcopy(obj: models.Model, **kwargs):
     n = obj.__class__(**kwargs)
     for f in obj._meta.fields:
         val = getattr(obj, f.name)
-        if isinstance(val, models.Model):
+        if isinstance(val, (models.Model, File)):
             setattr(n, f.name, copy.copy(val))
         else:
             setattr(n, f.name, copy.deepcopy(val))