[php-src] Issue #7961: strtotime returns non-sense integer given some timestamp string between Jan 17, 2022 and Jan 19, 2022

Issue: https://github.com/php/php-src/issues/7961 Comment Author: robert-h-at-cp @damianwadley Well, I'd say by reading the documentation [here](https://www.php.net/manual/en/function.strtotime.php), I didn't expect this function to be "garbage in, garbage out", but rather "garbage in, bool(false) out". I honestly didn't even expect it to be able to recognize Unix timestamps as it's not documented. And obviously there are developers out there using this function to validate potentially invalid strings, as we came across this issue in one of our dependent libraries ([source code here](https://github.com/johnbillion/extended-cpts/blob/develop/src/PostTypeAdmin.php#L989)).