Detect feature flags with the 'deduplicate' worker method as well

Signed-off-by: Rémy Coutable <remy@rymai.me>

rubocop/cop/gitlab/mark_used_feature_flags.rb

@@ -24,6 +24,7 @@ module RuboCop
         ].freeze
         WORKER_METHODS = %i[
           data_consistency
+          deduplicate
         ].freeze
         GRAPHQL_METHODS = %i[
           field

spec/rubocop/cop/gitlab/mark_used_feature_flags_spec.rb

@@ -203,6 +203,11 @@ RSpec.describe RuboCop::Cop::Gitlab::MarkUsedFeatureFlags do
     include_examples 'does not set any flags as used', 'data_consistency :delayed'
   end
 
+  describe 'Worker `deduplicate` method' do
+    include_examples 'sets flag as used', 'deduplicate :delayed, feature_flag: :foo', 'foo'
+    include_examples 'does not set any flags as used', 'deduplicate :delayed'
+  end
+
   describe 'GraphQL `field` method' do
     before do
       allow(cop).to receive(:in_graphql_types?).and_return(true)