Use cache_key for invalidating LC report

ee/app/models/software_license_policy.rb

@@ -53,10 +53,6 @@ class SoftwareLicensePolicy < ApplicationRecord
     LEGACY_CLASSIFICATION_STATUS.key(classification) || classification
   end
 
-  def self.workaround_cache_key
-    pluck(:id, :classification).flatten
-  end
-
   def self.to_classification(approval_status)
     LEGACY_CLASSIFICATION_STATUS.fetch(approval_status, approval_status)
   end

ee/app/services/ci/compare_license_scanning_reports_service.rb

@@ -17,7 +17,7 @@ module Ci
     private
 
     def key(base_pipeline, head_pipeline)
-      super(base_pipeline, head_pipeline) + project.software_license_policies.workaround_cache_key
+      super(base_pipeline, head_pipeline) + [project.software_license_policies.cache_key]
     end
   end
 end

ee/spec/models/merge_request_spec.rb

@@ -523,7 +523,7 @@ describe MergeRequest do
             expect_any_instance_of(Ci::CompareLicenseScanningReportsService)
                 .to receive(:execute).with(base_pipeline, head_pipeline).and_call_original
 
-            expect(subject[:key]).to include(*[license_1.id, license_1.classification, license_2.id, license_2.classification])
+            expect(subject[:key].last).to include("software_license_policies/query-")
           end
         end