Fix flaky search_results spec

What does this MR do and why?

Related to #491081 (closed)

Spec failures on master can be quickly reproduced with this subset of tests (thanks rspec --bisect!)

bundle exec rspec './ee/spec/lib/gitlab/elastic/search_results_spec.rb[1:5:4,1:5:5,1:5:6]' --seed 4145 -f d

This fixes a flaky few specs in ee/spec/lib/gitlab/elastic/search_results_spec.rb

The issue started happening when search_issues_uses_work_items_index was introduced, but the actual problem was the specs were not written to match how the code works.

The specs were setting public_and_internal_projects to false when initializing the class and performing a global search. Global search in EE with advanced search always sets this value to true.

The failure occurred because the routing was being set for requests because public_and_internal_projects was set to false

This MR changes the specs to use the default value (true) for public_and_internal_projects and updated results expectations to include public project results.

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Before	After

How to set up and validate locally

specs only