fix: make Repository::kind() detect linked worktrees of bare repos

[Jason Han (jason5122)]

Description

While bumping gix to v0.85 in tmux-sessionizer, I hit a misclassification for worktrees of bare repositories. Calling Repository::kind() returns Kind::Common, but it should be Kind::LinkedWorkTree.

Steps to Reproduce

mkdir -p /tmp/gix-bug && cd /tmp/gix-bug
git init --bare project
cd project
git worktree add ../worktree-of-project

// Move to `gix/examples/gix_bug.rs`.
// Usage: `cargo run -p gix --example gix_bug -- <path-to-worktree>`

use std::path::PathBuf;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let path = std::env::args_os()
        .nth(1)
        .map(PathBuf::from)
        .unwrap_or_else(|| ".".into());
    let repo = gix::open(&path)?;

    println!("kind(): {:?}", repo.kind());
    Ok(())
}

Before

$ cargo run -p gix --example gix_bug -- /tmp/gix-bug/worktree-of-project
kind(): Common

After

$ cargo run -p gix --example gix_bug -- /tmp/gix-bug/worktree-of-project
kind(): LinkedWorkTree