Draft: Removes OpenStruct use

What does this MR do and why?

Removes OpenStruct use in following files:

spec/factories/wiki_pages.rb
ee/spec/lib/gitlab/auth/group_saml/failure_handler_spec.rb

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #344279