docker/zig.sh: bump cargo-zigbuild 0.17.5 -> 0.23.4 so the zig image builds with Rust >= 1.98 (--fix-cortex-a53-843419)

[glaziermag]

The zig target of the CI workflow has failed at "Test Zig Image" on every push to main since Rust 1.98.0 (2026-08-20). The image installs cargo-zigbuild 0.17.5 (docker/zig.sh, unchanged since 2024-04), whose zig cc wrapper rejects the -Wl,--fix-cortex-a53-843419 linker argument that rustc now passes for every AArch64 Linux target (rust-lang/rust#155453, milestone 1.98.0). cargo-zigbuild filters that argument since 0.23.0 (rust-cross/cargo-zigbuild#451 / #452), so this bumps the pinned version and adapts the installer to the current release archives.

Failure on main (job target (zig,ubuntu-latest), run 35965047836, 2026-09-24, Rust 1.98.1):

error: linking with `/target/.zig-cache/cargo-zigbuild/0.17.5/zigcc-aarch64-unknown-linux-gnu.sh` failed: exit status: 1
  = note: error: unsupported linker arg: --fix-cortex-a53-843419
error: could not compile `hellopp` (bin "hellopp") due to 1 previous error

The same job was green on 2026-08-19 (run 32250555535, Rust 1.97.1); it has been red on both main pushes since (runs 35964074174 and 35965047836) and in the weekly runs.

Reproduction: cargo xtask build-docker-image zig followed by ./ci/test-zig-image.sh with a stable toolchain >= 1.98, exactly as the CI job does. On my fork, the same steps fail at HEAD (run 36208936418) and pass with this change (runs 36208937247 and 36209338211).

Changes in docker/zig.sh:

• cargo-zigbuild 0.17.5 -> 0.23.4.
• The release archives are now named cargo-zigbuild-<triple>.tar.xz and contain a cargo-zigbuild-<triple>/ directory, so the download URL, the tar flags and the extracted path change accordingly; the repository moved to rust-cross/cargo-zigbuild.
• Prebuilt Linux archives now exist only for x86_64 (gnu, musl) and aarch64 (gnu): linux/amd64 keeps the musl build, linux/arm64 uses the gnu build (the image is Ubuntu 24.04, so glibc is present), and linux/386 falls through to the existing cargo install path.

Zig stays at 0.11.0; cargo-zigbuild 0.23 still supports it. CI builds the image for linux/amd64 only, which is the path exercised by the fork run above.

Disclosure: this change was prepared with an AI coding agent (Claude Code); I reviewed the diff and the fork runs above are the verification.

[Emilgardis]

Please remove the co-authored-by for claude. This change is fine, but I don't want the implication of the attribution in this repo. This change is very small and there's no logic changed, only fixes.

[glaziermag]

Removed. The branch is now a single commit (47a82bc) with no co-authored-by trailer; the diff is unchanged.

Since merge commits here carry the PR description, I also dropped the "Generated with" footer line from it. The one-line disclosure is still in the description; tell me if you would rather that stay out of the merge message too and I will move it to a comment.