[ruby/irb] Close leaked pty IOs

https://github.com/ruby/irb/commit/cc9b1d7ba8

test/irb/test_debug_cmd.rb

@@ -223,6 +223,9 @@ module TestIRB
             end
           end
         end
+      ensure
+        read.close
+        write.close
       end
 
       lines.join