Fix test leak

Author: etiennebarrie

activerecord/test/cases/integration_test.rb

@@ -121,7 +121,7 @@ def test_param_delimiter_is_defined_per_class
     assert_equal("1;123", Cpk::Book.new(id: [1, 123]).to_param)
   ensure
     Cpk::Order.param_delimiter = old_order_delimiter
-    Cpk::Order.param_delimiter = old_book_delimiter
+    Cpk::Book.param_delimiter = old_book_delimiter
   end
 
   def test_cache_key_for_existing_record_is_not_timezone_dependent