Draft: Resolve "Improve code coverage of app/models/concerns/protected_ref.rb"

What does this MR do and why?

This MR adds missing coverage for the ProtectedRef.protected_ref_access_levels method as part of Improve code coverage around areas related to p... (&12239).

MR acceptance checklist

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

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Related to #435152