Fix EpicBaseEntity human_readable_timestamp

ee/app/serializers/epic_base_entity.rb

@@ -13,6 +13,6 @@ class EpicBaseEntity < Grape::Entity
     epic.end_date&.to_s(:medium)
   end
   expose :human_readable_timestamp, if: -> (epic, _) { epic.end_date.present? || epic.start_date.present? } do |epic|
-    remaining_days_in_words(epic)
+    remaining_days_in_words(epic.end_date, epic.start_date)
   end
 end

ee/spec/serializers/issue_serializer_spec.rb

@@ -10,7 +10,8 @@ describe IssueSerializer do
   end
 
   before do
-    create(:epic_issue, issue: resource)
+    epic = create(:epic, :use_fixed_dates)
+    create(:epic_issue, issue: resource, epic: epic)
   end
 
   context 'sidebar issue serialization' do