Make BackgroundTransaction#labels public

as are all other Transaction implementations

lib/gitlab/metrics/background_transaction.rb

@@ -6,8 +6,6 @@ module Gitlab
         @worker_class = worker_class
       end
 
-      protected
-
       def labels
         { controller: @worker_class.name, action: 'perform' }
       end

spec/lib/gitlab/metrics/background_transaction_spec.rb

@@ -10,4 +10,10 @@ describe Gitlab::Metrics::BackgroundTransaction do
       expect(subject.action).to eq('TestWorker#perform')
     end
   end
+
+  describe '#label' do
+    it 'returns labels based on class name' do
+      expect(subject.labels).to eq(controller: 'TestWorker', action: 'perform')
+    end
+  end
 end