Fix test pollution from simulate_saas rake task
What does this MR do and why?
The simulate_saas rake task redefines Gitlab.com? to return true. While it registers an at_exit hook to restore the method, this only runs when the Ruby process exits, not after each RSpec example.
This caused test pollution when graphql_introspection_rake_spec ran before other specs (like inactive_projects_deletion_cron_worker_spec) that depend on Gitlab.com? returning its original value.
Fix by capturing the original method before tests run and restoring it in an after hook.
References
How to set up and validate locally
Run the following:
bundle exec rspec './spec/tasks/gitlab/graphql_introspection_rake_spec.rb[1:3:1:1]' './spec/workers/projects/inactive_projects_deletion_cron_worker_spec.rb[1:1:2:1,1:1:2:4,1:1:2:5:1]' --seed 57942MR acceptance checklist
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