Fixed #31246 -- Fixed locking models in QuerySet.select_for_update(of=()) for related fields and parent link fields with multi-table inheritance.

Partly regression in 0107e3d105.

tests/select_for_update/models.py

@@ -1,7 +1,11 @@
 from django.db import models
 
 
-class Country(models.Model):
+class Entity(models.Model):
+    pass
+
+
+class Country(Entity):
     name = models.CharField(max_length=30)