update test code to ensure return value from class statement

test/t/class.rb

@@ -222,8 +222,8 @@ assert('Class new') do
   assert_equal(Class, Class.new.class)
 end
 
-assert('Class do not leak method') do
-  m = class C; def m; end; end
+assert('class to return the last value') do
+  m = class C; :m end
   assert_equal(m, :m)
 end