BUG: Error invalid path on valid git repo using `reftable` backend.

**Describe the bug**
`gitui` emit errors on some random(?) repo.

**To Reproduce**
Steps to reproduce the behavior:
1. Clone anything with Git 2.45+
2. Try to invoke `gitui` on it.
3. See error
```sh
$ gitui
invalid path
please run gitui inside of a non-bare git repository
```

**Expected behavior**
It should read the path as normal and pop out a TUI.

**Screenshots**

**Context (please complete the following information):**
- OS/Distro + Version: Windows 11 Pro x86_64 Build 10.0.26200.5761 (25H2)
- GitUI Version: gitui 0.27.0 2025-01-14 (99f6967)
- Rust version: Prebuilt on Releases.

**Additional context**
1. `lazygit` can consume that path just fine.
2. After trying to clone `gitui` to build locally with `rustc` version 1.89.0 (29483883e 2025-08-04), I got
```sh
Error: unsupported extension name extensions.refstorage; class=Repository (6)
```
3. Maybe it's `libgit2` error? please look more into it.
- Due to dependent on `git2`, `gitui` cant resolve `reftable` backend, and that's fine for me.