Fix RSpec/VerifiedDoubles cop (#25469)

spec/workers/regeneration_worker_spec.rb

@@ -9,7 +9,7 @@ describe RegenerationWorker do
     let(:account) { Fabricate(:account) }
 
     it 'calls the precompute feed service for the account' do
-      service = double(call: nil)
+      service = instance_double(PrecomputeFeedService, call: nil)
       allow(PrecomputeFeedService).to receive(:new).and_return(service)
       result = subject.perform(account.id)