Add missing conversation id for first response event (#2922)

- Add missing conversation id for first response event
- Fixing the flaky test

Fixes #2746

Co-authored-by: Tejaswini <tejaswini@chatwoot.com>

spec/builders/v2/report_builder_spec.rb

@@ -215,7 +215,7 @@ describe ::V2::ReportBuilder do
       end
 
       it 'returns average first response time' do
-        FactoryBot.create(:event, conversation: label_2.conversations.last, account: account, name: 'first_response')
+        label_2.events.update(value: 1.5)
 
         params = {
           metric: 'avg_first_response_time',