Ensure enum scopes work properly with STI and inheritance

The code was changed to call `where` on a specific class in 813c8c07,
but no reasoning was given and I can't see any good reason why we would
need to do that. This will ensure that the method is called on whatever
class the scope is called on.

Fixes #23013

activerecord/lib/active_record/enum.rb

@@ -187,7 +187,7 @@ def enum(definitions)
 
             # scope :active, -> { where status: 0 }
             klass.send(:detect_enum_conflict!, name, value_method_name, true)
-            klass.scope value_method_name, -> { klass.where name => value }
+            klass.scope value_method_name, -> { where(name => value) }
           end
         end
         defined_enums[name.to_s] = enum_values