Use NotesFinder#target to find Epics

lib/api/helpers/notes_helpers.rb

@@ -74,14 +74,14 @@ module API
       end
 
       def find_noteable(parent_type, parent_id, noteable_type, noteable_id)
-        params = params_by_noteable_type_and_id(noteable_type, noteable_id)
+        params = finder_params_by_noteable_type_and_id(noteable_type, noteable_id, parent_id)
 
-        noteable = NotesFinder.new(current_user, params.merge(project: user_project)).target
+        noteable = NotesFinder.new(current_user, params).target
         noteable = nil unless can?(current_user, noteable_read_ability_name(noteable), noteable)
         noteable || not_found!(noteable_type)
       end
 
-      def params_by_noteable_type_and_id(type, id)
+      def finder_params_by_noteable_type_and_id(type, id, parent_id)
         target_type = type.name.underscore
         { target_type: target_type }.tap do |h|
           if %w(issue merge_request).include?(target_type)
@@ -89,9 +89,15 @@ module API
           else
             h[:target_id] = id
           end
+
+          add_parent_to_finder_params(h, type, parent_id)
         end
       end
 
+      def add_parent_to_finder_params(finder_params, noteable_type, parent_id)
+        finder_params[:project] = user_project
+      end
+
       def noteable_parent(noteable)
         public_send("user_#{noteable.class.parent_class.to_s.underscore}") # rubocop:disable GitlabSecurity/PublicSend
       end