[php-src] Issue #7758: Datetime created from negative float timestamp is not monotonic (fraction part is added instead of substracted)

Issue: https://github.com/php/php-src/issues/7758 Author: mvorisek ### Description The following code: ```php foreach ([0.5, 0, -0.5, -1, -1.5] as $ts) { $date = new DateTime('@' . $ts); print_r($date); } ``` https://3v4l.org/i5hEN Diff of current output vs expected: ```diff DateTime Object ( [date] => 1970-01-01 00:00:00.500000 [timezone_type] => 1 [timezone] => +00:00 ) DateTime Object ( [date] => 1970-01-01 00:00:00.000000 [timezone_type] => 1 [timezone] => +00:00 ) DateTime Object ( - [date] => 1970-01-01 00:00:00.500000 + [date] => 1969-12-31 23:59:59.500000 [timezone_type] => 1 [timezone] => +00:00 ) DateTime Object ( [date] => 1969-12-31 23:59:59.000000 [timezone_type] => 1 [timezone] => +00:00 ) DateTime Object ( - [date] => 1969-12-31 23:59:59.500000 + [date] => 1969-12-31 23:59:58.500000 [timezone_type] => 1 [timezone] => +00:00 ) ``` present since PHP 8.0, should be fixed starting this version ### PHP Version PHP 8.0+ ### Operating System any