Use bookworm base image for glibc 2.36 compatibility

[kabdelhalem]

The current 13e658725d artifacts require glibc 2.38 and GLIBCXX 3.4.32, which limits deployment to Debian Trixie or Ubuntu 24.04+. Many embedded devices (e.g., Raspberry Pi) still run Debian 12 Bookworm.

Building with Bookworm produces artifacts requiring only:

• GLIBC_2.32
• GLIBCXX_3.4.29

Both are available in Debian 12 Bookworm (glibc 2.36, GLIBCXX 3.4.31).

I have tested changes by building artifacts locally and verifying artifact requirements via objdump -T:
- Max GLIBC required: 2.32
- Max GLIBCXX required: 3.4.29

Ref: flutter-elinux/flutter-elinux#2 (discussion about rebuilding with older distro for compatibility)

[martinetd]

Thanks!

I actually have a couple of commits ready to go back all the way to bullseye (hinted at this in #2), just wanted to confirm it works when running on a newer release first (not expecting any problem on the glibc side, but the artifacts also link with libwayland and other system libraries which might not be as stable)

Ultimately I think the best way forward would be to just not use pre-built flutter-embedded-linux binaries, I'm not sure why the project is setup like this -- the embedder itself is pretty quick to build so there's no much time saving here and it's the only way to be sure it's appropriate for your target... But that's going to take more time, so building with an older distro is a good first step

[martinetd]

(closing as superceeded by #9)