Fix an array comparison flaky spec

What does this MR do and why?

The error message implies there's an order issue when doing comparison.

Failures:
  1) Search::RakeTaskExecutorService#index_work_items with limited indexing enabled does not call track! for work_items that should not be indexed
     Failure/Error: unscoped { yield relation, index }
       #<Elastic::ProcessBookkeepingService (class)> received :track! with unexpected arguments
         expected: (#<WorkItem id:119 group5#1>, #<WorkItem id:121 group7#1>)
              got: (#<WorkItem id:121 group7#1>, #<WorkItem id:119 group5#1>)
       Diff:
       @@ -1 +1 @@
       -[#<WorkItem id:119 group5#1>, #<WorkItem id:121 group7#1>]
       +[#<WorkItem id:121 group7#1>, #<WorkItem id:119 group5#1>]
     # ./ee/app/services/search/rake_task_executor_service.rb:384:in `block in index_work_items'
     # ./app/models/concerns/each_batch.rb:99:in `block (2 levels) in each_batch'
     # ./app/models/concerns/each_batch.rb:99:in `block in each_batch'
     # ./app/models/concerns/each_batch.rb:69:in `step'
     # ./app/models/concerns/each_batch.rb:69:in `each_batch'
     # ./ee/app/services/search/rake_task_executor_service.rb:383:in `index_work_items'
     # ./ee/app/services/search/rake_task_executor_service.rb:48:in `execute'
     # ./ee/spec/services/search/rake_task_executor_service_spec.rb:699:in `block (4 levels) in <top (required)>'

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Related to #474157 (closed)