PHP 8.4 support

[pfrenssen]

It would be great if we could have a PHP 8.4 buildpack. PHP 8.3 went out of active support on December 31, 2025 and is now only receiving security fixes.

[ramonskie]

there are users currently experiencing issue with the 5.x release
we need to solve that first see #1208

im also looking for testers for the 5.x release so we can debug this faster,
would you be interested?