De-quarantine project activity test

qa/qa/specs/features/browser_ui/1_manage/project/view_project_activity_spec.rb

 # frozen_string_literal: true
 
 module QA
-  # Failure issue: https://gitlab.com/gitlab-org/quality/staging/issues/21
-  context 'Manage', :quarantine do
+  context 'Manage' do
     describe 'Project activity' do
       it 'user creates an event in the activity page upon Git push' do
         Runtime::Browser.visit(:gitlab, Page::Main::Login)