Improve reader check

Author: flash-gordon

repository/lib/rom/repository/class_interface.rb

@@ -59,7 +59,7 @@ def [](name)
       def new(container = nil, root: Undefined, **options)
         container ||= options.fetch(:container)
 
-        if ancestors.none? { |ancestor| ancestor.is_a?(relation_reader) }
+        unless relation_reader.added_to?(self)
           include relation_reader.new(
             relations: container.relations.elements.keys,
             cache: container.cache,

repository/lib/rom/repository/relation_reader.rb

@@ -4,6 +4,10 @@ module ROM
   class Repository
     # @api private
     class RelationReader < ::Module
+      def self.added_to?(klass)
+        klass < InstanceMethods
+      end
+
       module InstanceMethods
         extend ::Dry::Core::Deprecations[:'rom-repository']