[php-src] Issue #24669: Surfacing security issues with OpenBSD as part of the CI with hardened memory allocator

Issue: https://github.com/php/php-src/issues/24669 Author: loganaden ### Description Hi folks, We are analysing the PHP code and while it's clear that there are performance benefits from PHP current ZendMM allocator, we also see benefits from disabling it as a build option to surface memory corruption security bugs. OpenBSD has a hardened memory allocator which can surface a lot of those security issues: [OpenBSD malloc](https://www.openbsd.org/papers/eurobsdcon2023-otto-malloc.pdf) Would the PHP team be willing to accept a PR for the CI which adds OpenBSD as a runner for CI builds with USE_ZEND_ALLOC=0 activated ?