Description:
------------
Maybe it is not a mistake, but I would like a consistent handling here. If 5-digit years are not desired, they should not be entered, otherwise it would be desirable that I can unserialize serialized objects, which contain 5-digit years

Tested with php 7.2, 7.3 and 7.4.



Thank you.

Test script:
---------------
<?php
  
$the_date = new DateTime();
$the_date->setTime(0, 0, 0);
$the_date->SetDate(20201, 01, 01);

var_dump($the_date);

$serialized = serialize($the_date);
var_dump($serialized);
var_dump(unserialize($serialized));

Actual result:
--------------
/home/nico/test/unserialize.php:7:
class DateTime#1 (3) {
  public $date =>
  string(27) "20201-01-01 00:00:00.000000"
  public $timezone_type =>
  int(3)
  public $timezone =>
  string(13) "Europe/Berlin"
}
/home/nico/test/unserialize.php:10:
string(126) "O:8:"DateTime":3:{s:4:"date";s:27:"20201-01-01 00:00:00.000000";s:13:"timezone_type";i:3;s:8:"timezone";s:13:"Europe/Berlin";}"
PHP Fatal error:  Uncaught Error: Invalid serialization data for DateTime object in /home/nico/test/unserialize.php:11
Stack trace:
#0 [internal function]: DateTime->__wakeup()
#1 /home/nico/test/unserialize.php(11): unserialize('O:8:"DateTime":...')
#2 {main}
  thrown in /home/nico/test/unserialize.php on line 11