Revert using unavailable constants for import test

qa/qa/specs/features/ee/api/1_manage/migration/gitlab_migration_group_spec.rb

@@ -39,8 +39,8 @@ def find_epic(epics, title)
             labels: 'label1,label2',
             parent_id: parent_epic.id)
 
-          child_epic.award_emoji(AwardEmoji::THUMBS_UP)
-          child_epic.award_emoji(AwardEmoji::THUMBS_DOWN)
+          child_epic.award_emoji("thumbsup")
+          child_epic.award_emoji("thumbsdown")
 
           source_iteration
         end