[ruby/irb] Consume the warning for non-existent history path

Fix ruby/irb#852 (comment)

ruby/irb@9a7e060e57

Author: nobu

test/irb/test_history.rb

@@ -173,7 +173,7 @@ def test_history_does_not_raise_when_history_file_directory_does_not_exist
       IRB.conf[:HISTORY_FILE] = "fake/fake/fake/history_file"
       io = TestInputMethodWithRelineHistory.new
 
-      assert_nothing_raised do
+      assert_warn(/history file does not exist/) do
         io.save_history
       end
     ensure