Runtime modification of parent serializer attributes doesn't update child attributes

[orlando]

This is more of a question, since I'm not sure you want to support this use case. This is related to an issue with Discourse - https://meta.discourse.org/t/inconsistent-behaviour-in-plugins-between-development-and-production/87220

Expected behavior vs actual behavior

If you call attributes in a parent serializer after you defined a child serializer, changes to the parent will not be reflected in child attributes

class ParentSerializer < ActiveModel::Serializer
  attributes :name
end

class ChildSerializer < ParentSerializer
  attributes :email
end

ParentSerializer.attributes(:last_name)

Actual

ParentSerializer._attributes =>  {:name=>:name, :last_name=>:last_name}
ChildSerializer._attributes =>  {:name=>:name, :email=>:email} 

Expected

ParentSerializer._attributes =>  {:name=>:name, :last_name=>:last_name}
ChildSerializer._attributes =>  {:name=>:name, :email=>:email, :last_name=>:last_name} 

Steps to reproduce

I made a failing test case https://github.com/orlando/active_model_serializers/commit/91408c9ac2ed9167a8c480fdbad3b6889e2e38b9

Environment

ActiveModelSerializers Version 0.8.4: