git2-rs fails to verify SSH keys by default

Summary

The git2 and libgit2-sys crates are Rust wrappers around the [libgit2](https://libgit2.org/) C library. It was discovered that libgit2 1.5.0 and below did not verify SSH host keys when establishing an SSH connection, exposing users of the library to Man-In-the-Middle attacks. The libgit2 team assigned [CVE-2023-22742](https://github.com/libgit2/libgit2/security/advisories/GHSA-8643-3wh5-rmjq) to this vulnerability. The following versions of the libgit2-sys Rust crate have been released: * libgit2-sys 0.14.2, updating the underlying libgit2 C library to version 1.5.1. * libgit2-sys 0.13.5, updating the underlying libgit2 C library to version 1.4.5. A new git2 crate version has also been released, 0.16.1. This version only bumps its libgit2-sys dependency to ensure no vulnerable libgit2-sys versions are used, but contains no code changes: if you update the libgit2-sys version there is no need to also update the git2 crate version. [You can learn more about this vulnerability in libgit2's advisory](https://github.com/libgit2/libgit2/security/advisories/GHSA-8643-3wh5-rmjq)