Replace deprecated gmstrftime with gmdate

[elidrissidev]

Description (*)

Replaces gmstrftime which is deprecated starting from PHP 8.1 with gmdate.

Fixed Issues (if relevant)

1. Fixes Replace deprecated strftime and gmstrftime PHP functions #2030

Manual testing scenarios (*)

<?php

date_default_timezone_set('Europe/Amsterdam'); // GMT+1

echo date('Y-m-d H:i:s', mktime(0, 0, 0, 1, 1, 1998)) . PHP_EOL;
// > 1998-01-01 00:00:00 (from Europe/Amsterdam timezone)
echo gmdate('Y-m-d H:i:s', mktime(0, 0, 0, 1, 1, 1998)) . PHP_EOL;
// > 1997-12-31 23:00:00 (from UTC timezone)
echo gmstrftime("%Y-%m-%d %H:%M:%S", mktime(0, 0, 0, 1, 1, 1998)) . PHP_EOL;
// > 1997-12-31 23:00:00 (from UTC timezone)

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[elidrissidev]

phpstan fails due to unrelated change (#2861).

[fballiano]

merged and cherrypicked to v20