In order to migrate PHP workloads to bookworm, we need to rebuild the PHP packages for it. This will use the bookworm-native versions of ICU (72) and PCRE2 (i.e., rather than the backports thereof we use under bullseye, which are no longer needed).
The plan is to include those packages in component/php83 so that we can switch the php8.3 image stack to bookworm in-place, and deprecate the temporary php8.3-icu72 stack (along with component/php83-icu72). More details on the high-level plan in T418200#11877390.