Fix index_projects_by_range_service_spec failure

What does this MR do?

This MR should fix ee/spec/services/elastic/index_projects_by_range_service_spec.rb:8 failure in the 14-2-stable-ee branch

6) Elastic::IndexProjectsByRangeService#execute when without project does not err
     Failure/Error: described_class.new.execute
       (ElasticFullIndexWorker (class)).bulk_perform_async([[1, 1000], [1001, 1054]])
           expected: 0 times with any arguments
           received: 1 time with arguments: ([[1, 1000], [1001, 1054]])
     # ./ee/app/services/elastic/index_projects_by_range_service.rb:21:in `block in execute'
     # ./ee/app/services/elastic/index_projects_by_range_service.rb:20:in `each'
     # ./ee/app/services/elastic/index_projects_by_range_service.rb:20:in `each_slice'
     # ./ee/app/services/elastic/index_projects_by_range_service.rb:20:in `execute'
     # ./ee/spec/services/elastic/index_projects_by_range_service_spec.rb:11:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:390:in `block (3 levels) in <top (required)>'
     # ./spec/support/sidekiq_middleware.rb:9:in `with_sidekiq_server_middleware'
     # ./spec/spec_helper.rb:381:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:377:in `block (3 levels) in <top (required)>'
     # ./lib/gitlab/application_context.rb:31:in `with_raw_context'
     # ./spec/spec_helper.rb:377:in `block (2 levels) in <top (required)>'

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