Fix flaky board_filters_spec search bar timing

What does this MR do and why?

Fix flaky board_filters_spec search bar timing

The filtered search bar remounts under a new Vue key whenever the board GraphQL query resolves, which invalidates any element already found inside it and closes an open suggestions dropdown. The spec called wait_for_requests right after visiting the board, but that helper only checks that no requests are currently in flight, so it could return before the board queries were even issued, leaving the spec typing into a search bar that was about to be torn down and rebuilt. Waiting for the board lists to load first guarantees those queries have completed, and no longer memoizing the search bar wrapper means it gets re-found after any rebuild instead of going stale.

References

• https://gitlab.com/gitlab-org/quality/test-failure-issues/-/work_items/44269

Screenshots or screen recordings

Not provided

How to set up and validate locally

bundle exec rspec spec/features/boards/board_filters_spec.rb

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