In advance of the PHP 8.3 migration, we'll need to configure the WikimediaEvents extension (see phpEngine.js) to set the PHP_ENGINE=8.3 Cookie value based on the desired (initially zero) consistent enrollment fraction.
This is a fairly straightforward mediawiki-config change to set WMENewPHPVersion and WMENewPHPSamplingRate, similar to https://gerrit.wikimedia.org/r/1080388 during the 8.1 migration.