chore(deps): update git2 to use libgit2 1.9

[chenrui333]

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes

[thoughtpolice]

There isn't a build of libgit2 1.9 for Nix yet, so I'm not sure we want to pull the trigger on this just yet. Or we need to update the Flake to build libgit2 out-of-band.

[chenrui333]

I did not know that nix did not have a libgit2 1.9 build yet, but yeah, this PR can certainly wait for libgit2 1.9 on the nix side.

[alerque]

For the flake you should be able to just temporarily the LIBGIT2_NO_VENDOR=1 so that the libgit2-sys crate vendors the build, then when nixpkgs can be update to something with libgit2-1.9 you can go back to forcing it to not vendor it.

[PhilipMetzger]

Can you also please adhere to the commit style outlined by this document here: https://github.com/jj-vcs/jj/blob/main/docs/contributing.md#code-reviews. Thanks, my suggestion is either cargo: like dependabot or deps: which you already have.

[emilazy]

There isn't a build of libgit2 1.9 for Nix yet, so I'm not sure we want to pull the trigger on this just yet. Or we need to update the Flake to build libgit2 out-of-band.

There’s a bit of a catch‐22 here: NixOS/nixpkgs#373096 updates libgit2 to 1.9.0, but of course by the time it hits the channels it’ll break our Jujutsu package.

I guess we can apply this patch on the Nixpkgs end for now to break the cycle.

[alerque]

The git2 crate ever only supporting one release cycle at a time is really rather a pain.

As the Arch Linux packager working through the libgit2-1.9 todo list, I can say we're probably going to have to provide a 1.8 compat package for a while. Nix may end up having to do the same, there are a few upstream projects that are not easily patched one direction or the other. Jujutsu was pretty easy (we just back ported this bump and everything worked) but some other tools are not playing so nice.