Add Debian 13 (Trixie) support

[GreyXor]

Describe your feature request

Debian 13 (Trixie) is currently scheduled for release on August 9th, as per Debian's official announcement.

This issue is to track and prepare support for frankenphp Docker images based on Debian 13 once it becomes available in the official mirrors.

Keeping up with upstream base image releases ensures long-term supportability, access to the latest system libraries, and security improvements.

Thanks for your great work maintaining this image!

Context: docker-library/php#1596

[AlliBalliBaba]

I'm all for supporting the new debian version as soon as it's supported upstream👍

Would we drop bookworm then or support both @dunglas @withinboredom ?

[dunglas]

We could align on the official PHP images for that.

[zip-fa]

Hey, any news on this?

[GreyXor]

Hey, any news on this?

I'm not sure. I don't know if we need something else but the branch is ready and working.

[AlliBalliBaba]

I think the PR is ready to go, just waiting for @dunglas to create a new release.