Fix flaky MergeRequestUserEntity test

spec/serializers/merge_request_user_entity_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe MergeRequestUserEntity do
-  let_it_be(:user) { create(:user) }
+  let_it_be_with_reload(:user) { create(:user) }
   let_it_be(:merge_request) { create(:merge_request, assignees: [user]) }
 
   let(:request) { EntityRequest.new(project: merge_request.target_project, current_user: user) }