Retry store_lti_session_data

We need to store or update the LTI parameters. However, this operation is not atomic and multiple requests can interfere with our database operation. Therefore, we need to retry in case the record is not unique.

Fixes CODEOCEAN-TC

app/controllers/concerns/lti.rb

@@ -225,6 +225,8 @@ module Lti
     @lti_parameters.save!
 
     session[:external_user_id] = current_user.id
+  rescue ActiveRecord::RecordNotUnique
+    retry
   end
 
   private :store_lti_session_data