Linux release packages require glibc 2.39, failing on older distros #1256

The prebuilt Linux packages (RPM, DEB, AppImage) fail to start on any distro with glibc < 2.39 — e.g. Fedora 39 (glibc 2.38) reports /lib64/libc.so.6: version GLIBC_2.39' not found.

Root cause: the Package CI installs cross from git main (cargo install cross --git …), which now uses the Ubuntu 24.04-based :main images (glibc 2.39).
Since the build job's binary feeds all three Linux packages, they all inherit that floor.
This is a regression from an upstream cross image bump, not a repo change: cross-rs/cross#1779

Root cause identified: our CI builds Linux binaries with cross installed from git main, whose images moved to an Ubuntu 24.04 base (glibc 2.39) — so the artifacts inherit a glibc 2.39 floor and won't run on older distros like Fedora 39 (glibc 2.38).

There's no quick pin that fixes it: the only older cross image tag is EOL Ubuntu 16.04 (missing needed packages), and the glibc friendly 20.04/22.04 images only ever existed on the moving main tag, so there's nothing stable to pin to.

We also tried cargo-zigbuild targeting glibc 2.28: it builds fine after some tweaks, but linking sniffnet (glibc 2.28) against the runner's newer libasound / libpcap (glibc 2.34+) fails at link time.