[ruby/fileutils] A workaround for RBS

ruby/fileutils@fde0f0713a

Author: nobu

lib/fileutils.rb

@@ -2473,6 +2473,7 @@ def fu_each_src_dest(src, dest)   #:nodoc:
   def fu_each_src_dest0(src, dest, target_directory = true)   #:nodoc:
     if tmp = Array.try_convert(src)
       unless target_directory or tmp.size <= 1
+        tmp = tmp.map {|f| File.path(f)} # A workaround for RBS
         raise ArgumentError, "extra target #{tmp}"
       end
       tmp.each do |s|