Fix static-analysis offenses in QA support class

qa/qa/scenario/taggable.rb

 module QA
   module Scenario
     module Taggable
+      # rubocop:disable Gitlab/ModuleWithInstanceVariables
+
       def tags(*tags)
         @tags = tags
       end
@@ -8,6 +10,8 @@ module QA
       def focus
         @tags.to_a
       end
+
+      # rubocop:enable Gitlab/ModuleWithInstanceVariables
     end
   end
 end