Fixed #28462 -- Decreased memory usage with ModelAdmin.list_editable.

Regression in 917cc288a3.

tests/admin_changelist/models.py

@@ -1,3 +1,5 @@
+import uuid
+
 from django.db import models
 
 
@@ -73,6 +75,7 @@ class Invitation(models.Model):
 
 
 class Swallow(models.Model):
+    uuid = models.UUIDField(primary_key=True, default=uuid.uuid4)
     origin = models.CharField(max_length=255)
     load = models.FloatField()
     speed = models.FloatField()