fix(release): build Linux CLI on ubuntu-22.04 (glibc 2.35) so binaries run on older distros

[r266-tech]

Problem (#2321)

The released Linux hindsight CLI binaries are built by the release-rust-cli job on glibc-2.39 GitHub runners:

• x86_64-unknown-linux-gnu → ubuntu-latest (= Ubuntu 24.04, glibc 2.39)
• aarch64-unknown-linux-gnu → ubuntu-24.04-arm (glibc 2.39)

cargo build --release links dynamically against the build host's glibc, so the shipped binary requires GLIBC_2.39, which only Ubuntu 24.04 / Debian 13 provide. On anything older it fails at startup exactly as reported:

hindsight: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.39' not found (required by hindsight)

Fix

Pin both Linux build legs to ubuntu-22.04 (glibc 2.35), the oldest GitHub-hosted Ubuntu runner:

• ubuntu-latest → ubuntu-22.04 (amd64)
• ubuntu-24.04-arm → ubuntu-22.04-arm (arm64)

ubuntu-22.04-arm is a maintained GitHub-hosted arm64 runner label (actions/runner-images), so the arm64 leg keeps shipping. No Cargo.toml / TLS / dependency changes. macOS targets are untouched.

This restores runnability on Ubuntu 22.04+, Debian 12, RHEL/Rocky/Alma 9, etc.

Scope / what this does not cover

The reporter's ### Option A suggested Ubuntu 20.04 (glibc 2.31), but GitHub retired the ubuntu-20.04 hosted runner in April 2025, so 22.04 (glibc 2.35) is the lowest floor reachable with hosted runners. This therefore does not fix systems on glibc < 2.35 — Ubuntu 20.04 (2.31), Debian 11, RHEL/CentOS 8 (2.28), or Alpine.

For full coverage including those, the reporter's ### Option B (the fully-static x86_64-unknown-linux-musl target) is the complete fix. That's a larger change — hindsight-cli pulls reqwest with default features (native-tls/OpenSSL), so musl-static would mean default-features = false + rustls-tls, i.e. a TLS-stack swap worth reviewing on its own. Happy to send that as a follow-up if you'd prefer the broader floor; this PR is the clean, low-risk improvement that fixes the large majority of current LTS/enterprise deployments.

Addresses #2321 (leaving the issue open in case you want the musl path for glibc < 2.35).

[nicoloboschi]

LGTM. glibc backward-compat means binaries built on 2.35 run on 2.35+ (incl. current 24.04 runners), so this strictly widens compatibility with no regression. ubuntu-22.04-arm is a valid hosted arm64 label. OpenSSL/musl full-portability path correctly deferred to the Option B follow-up.