Fix search feature specs with super sidebar

What does this MR do and why?

Screenshots or screen recordings

No visual change.

How to set up and validate locally

bundle exec rspec spec/features/search/user_uses_header_search_field_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 #420121 (closed)