Fix RSpec/LetSetup cop in ap/fetch_featured_collection_service (#28461)

.rubocop_todo.yml

@@ -48,7 +48,6 @@ RSpec/ExampleLength:
 RSpec/LetSetup:
   Exclude:
     - 'spec/models/account_statuses_cleanup_policy_spec.rb'
-    - 'spec/services/activitypub/fetch_featured_collection_service_spec.rb'
 
 RSpec/MultipleExpectations:
   Max: 8

spec/services/activitypub/fetch_featured_collection_service_spec.rb

@@ -87,6 +87,7 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
         'https://example.com/account/pinned/unknown-inlined',
         'https://example.com/account/pinned/unknown-reachable'
       )
+      expect(actor.pinned_statuses).to_not include(known_status)
     end
   end