Skip test that depends on RubyVM when it is not available (JRuby).

activesupport/test/executor_test.rb

@@ -192,6 +192,8 @@ def test_hook_insertion_order
   end
 
   def test_class_serial_is_unaffected
+    skip if !defined?(RubyVM)
+
     hook = Class.new do
       define_method(:run) do
         nil