Remove require that was loading PipelineMessage twice

spec/support/shared_examples/slack_mattermost_notifications_shared_examples.rb

 # frozen_string_literal: true
 
-Dir[Rails.root.join("app/models/project_services/chat_message/*.rb")].each { |f| require f }
-
 RSpec.shared_examples 'slack or mattermost notifications' do |service_name|
   let(:chat_service) { described_class.new }
   let(:webhook_url) { 'https://example.gitlab.com/' }