Mark Namespaces::RootStatisticsWorker idempotent

This worker was already idempotent, this marks it as such so we can
deduplicate it later.

app/workers/all_queues.yml

@@ -884,7 +884,7 @@
   :urgency: :low
   :resource_boundary: :unknown
   :weight: 1
-  :idempotent: 
+  :idempotent: true
 - :name: update_namespace_statistics:namespaces_schedule_aggregation
   :feature_category: :source_code_management
   :has_external_dependencies: 

app/workers/namespaces/root_statistics_worker.rb

 # frozen_string_literal: true
 
 module Namespaces
-  class RootStatisticsWorker # rubocop:disable Scalability/IdempotentWorker
+  class RootStatisticsWorker
     include ApplicationWorker
 
     queue_namespace :update_namespace_statistics
     feature_category :source_code_management
+    idempotent!
 
     def perform(namespace_id)
       namespace = Namespace.find(namespace_id)

spec/workers/namespaces/root_statistics_worker_spec.rb

@@ -74,4 +74,19 @@ describe Namespaces::RootStatisticsWorker, '#perform' do
       worker.perform(group.id)
     end
   end
+
+  it_behaves_like 'an idempotent worker' do
+    let(:job_args) { [group.id] }
+
+    it 'deletes one aggregation schedule' do
+      # Make sure the group and it's aggregation schedule are created before
+      # counting
+      group
+
+      expect { worker.perform(*job_args) }
+        .to change { Namespace::AggregationSchedule.count }.by(-1)
+      expect { worker.perform(*job_args) }
+        .not_to change { Namespace::AggregationSchedule.count }
+    end
+  end
 end