Do not double "yp_" prefix [ci skip]

tool/sync_default_gems.rb

@@ -412,6 +412,7 @@ module SyncDefaultGems
       # Move all files in enc to be prefixed with yp_ in order
       # to deconflict them from non-yarp enc files
       (Dir.entries("yarp/enc/") - ["..", "."]).each do |f|
+        next if f.start_with?("yp_")
         mv "yarp/enc/#{f}", "yarp/enc/yp_#{f}"
       end