Memoize spdx_identifiers method

ee/app/services/package_metadata/ingestion/compressed_package/license_ingestion_task.rb

@@ -4,6 +4,8 @@ module PackageMetadata
   module Ingestion
     module CompressedPackage
       class LicenseIngestionTask
+        include ::Gitlab::Utils::StrongMemoize
+
         def initialize(import_data, license_map)
           @import_data = import_data
           @license_map = license_map
@@ -27,15 +29,16 @@ def execute
         attr_reader :import_data
         attr_accessor :license_map
 
+        def spdx_identifiers
+          import_data.flat_map(&:spdx_identifiers).sort.uniq
+        end
+        strong_memoize_attr :spdx_identifiers
+
         def existing_licenses
           PackageMetadata::License.with_spdx_identifiers(spdx_identifiers)
             .to_h { |license| [license.spdx_identifier, license.id] }
         end
 
-        def spdx_identifiers
-          import_data.flat_map(&:spdx_identifiers).sort.uniq
-        end
-
         def new_licenses
           spdx_identifiers
             .reject { |id| license_map[id] }

ee/spec/services/package_metadata/compressed_package_data_object_spec.rb

@@ -142,7 +142,7 @@
     subject(:spdx_identifiers) { obj.spdx_identifiers }
 
     it 'sorts licenses and removes duplicates' do
-      expect(obj.spdx_identifiers).to eq(%w[Apache-1.1 CC-PDDC unknown])
+      expect(spdx_identifiers).to eq(%w[Apache-1.1 CC-PDDC unknown])
     end
 
     # See https://gitlab.com/gitlab-org/gitlab/-/issues/418114