Improve Vulnerability Findinds code quality

ee/lib/api/vulnerability_findings.rb

@@ -3,15 +3,20 @@
 module API
   class VulnerabilityFindings < Grape::API
     include PaginationParams
+    include ::Gitlab::Utils::StrongMemoize
 
     helpers do
-      def vulnerability_occurrences_by(params)
-        pipeline = if params[:pipeline_id]
-                     user_project.all_pipelines.find_by(id: params[:pipeline_id]) # rubocop:disable CodeReuse/ActiveRecord
-                   else
-                     user_project.latest_pipeline_with_security_reports
-                   end
+      def pipeline
+        strong_memoize(:pipeline) do
+          if params[:pipeline_id]
+            user_project.all_pipelines.for_id(params[:pipeline_id]).first
+          else
+            user_project.latest_pipeline_with_security_reports
+          end
+        end
+      end
 
+      def vulnerability_occurrences_by(params)
         return [] unless pipeline
 
         aggregated_report = Security::PipelineVulnerabilitiesFinder.new(pipeline: pipeline, params: params).execute