Update CORE_PHP_MAX to 8.4

Issue information

From user: berdir

Related to !312 (merged) !311 (merged)

Contribution record

Fork management

Problem/Motivation

Drupal 10.4 (maybe latest dev only at the moment) and 11.1 now support PHP 8.4 and people are filling issues about PHP 8.4 deprecation in contrib projects: #3495869: Deprecations PHP 8.4

Lets update the variable so that it's easy to test that.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes