Improved naming consistency in BaseManage.contribute_to_class().

Matches signatures of other contribute_to_class() methods.

django/db/models/manager.py

@@ -109,13 +109,13 @@ class BaseManager:
             **cls._get_queryset_methods(queryset_class),
         })
 
-    def contribute_to_class(self, model, name):
+    def contribute_to_class(self, cls, name):
         self.name = self.name or name
-        self.model = model
+        self.model = cls
 
-        setattr(model, name, ManagerDescriptor(self))
+        setattr(cls, name, ManagerDescriptor(self))
 
-        model._meta.add_manager(self)
+        cls._meta.add_manager(self)
 
     def _set_creation_counter(self):
         """