Step-up auth: Make conditions evaluation more readable

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What does this MR do and why?

[skip ci] Step-up auth: Make conditions evaluation more readable

This commit addresses the suggestion from @atevans, see !187491 (comment 2547835827)

Changelog: other

🛠️ with ❤️ at Siemens

References

• !187491 (comment 2547835827)

Screenshots or screen recordings

Only refactor and no changes in the behavior.

How to set up and validate locally

1. Run the relevant test

   bundle exec rspec spec/lib/gitlab/auth/oidc/step_up_authentication_spec.rb

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

MR Checklist (@gerardo-navarro)

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the style guides
• Conforms to the javascript style guides
• Conforms to the database guides
• Conforms to the merge request performance guidelines

Related to #474650