Currently we use PHP packages from packages.sury.org. While the WMF images are going to be similar (as per T398245: Prepare WMF PHP 8.3 packages for bullseye), there may be differences like ICU versions.
So with PHP 8.3 intending to be the next WMF deployed version of PHP after PHP 8.1, we should move CI to using the WMF images for comparable-ness with deployment.