refactor: valid_date does not work in PHP 8.2

[kenjis]

Description
See #6170
See #6172 (comment)

bash-3.2$ ./phpunit tests/system/Validation/FormatRulesTest.php
PHPUnit 9.5.25 #StandWithUkraine

Runtime:       PHP 8.2.0-dev
Configuration: /Users/kenji/work/codeigniter/official/CodeIgniter4/phpunit.xml

...............................................................  63 / 193 ( 32%)
............................................................... 126 / 193 ( 65%)
............................................................... 189 / 193 ( 97%)
....                                                            193 / 193 (100%)

Time: 00:00.325, Memory: 14.00 MB

OK (193 tests, 193 assertions)

Checklist:

• Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• [] User guide updated
• Conforms to style guide

[paulbalandan]

Is there a case where $date is a DateTime instance yet $errors contains actual errors? If no, then can we remove the getLastErrors check?

[kenjis]

Is there a case where $date is a DateTime instance yet $errors contains actual errors?

Yes.

            [
                '1991-02-29',
                'Y-m-d',
                false,
            ],
            [
                'Thu, 31 Jun 2013 13:31:00',
                'D, d M Y H:i:s',
                false,
            ],
            [
                '2, 17, 2001',
                'j, n, Y',
                false,
            ],
            [
                '09-42-25, 12-00-17',
                'h-i-s, j-m-y',
                false,
            ],

[samsonasik]

Thank you @kenjis