[php-src] Issue #8260: Adding a DateInterval during switch to DST can result in incorrect times

Issue: https://github.com/php/php-src/issues/8260 Author: timmipetit ### Description Behaviour in PHP 8.1 is correct, but incorrect for PHP 8.0.17: https://3v4l.org/HQmqn The following code: ```php <?php date_default_timezone_set('Europe/Amsterdam'); $baseDate = new DateTimeImmutable('2022-03-27 01:30:00'); echo $baseDate->add(new DateInterval('PT1H'))->format('Y-m-d H:i:s') . PHP_EOL; echo $baseDate->add(new DateInterval('PT2H'))->format('Y-m-d H:i:s') . PHP_EOL; echo $baseDate->add(new DateInterval('PT1H'))->add(new DateInterval('PT1H'))->format('Y-m-d H:i:s') . PHP_EOL; ``` Resulted in this output: ``` 2022-03-27 03:30:00 2022-03-27 03:30:00 2022-03-27 04:30:00 ``` But I expected this output instead: ``` 2022-03-27 03:30:00 2022-03-27 04:30:00 2022-03-27 04:30:00 ``` ### PHP Version PHP 8.0.17 ### Operating System _No response_