Stashing tab shows not staged/ not tracked files in view

Hi,

I'm not sure it's even a bug.

When I was doing stashing in Stash[4] tab, you can switch what to stash by toggling staged/untracked files with keys `i/u` respectively.

At first I thought it's noop, since there was no visual indication or cue that anything changed. It works as it should by omitting untracked or staged files when toggling with respective keys.

I figured out that it behaves correctly without any obvious clue only by accident.
I had a single untracked directory with different user. The directory had `root` user and I couldn't stash it cause of permissions. Than the window popped up showing when I was attempting to stash with stashing configuration `{StashUntracked: true, ...}`. When pressing `u`, the config changed and I could stash only tracked files as expected.

**To Reproduce**
Create staged or untracked files with elevated permission like `root` in project folder. Notice error, than press u or i and see it stashes as expected.

**Expected behavior**
I expect to have visual cue for what will be stashed. It should be reflected in the file tree view upon pressing `i/u` keys.

**Screenshots**
The below screenshot actually show correct behavious, as there's nothing to stash, but files are still listed in file tree view

**Context (please complete the following information):**
- OS/Distro + Version: `Fedora Linux 39 (Workstation Edition) x86_64`
- GitUI Version `nightly 2024-06-09 ()`
- Rust version: `1.74.0-x86_64-unknown-linux-gnu`

Start by reproducing the behavior in gitui's Stash tab with staged and untracked files, then trace the i/u key handling and the file tree view. Done means the tree visibly indicates which staged or untracked files will be included after either toggle, while the existing stashing behavior remains correct.

索引モデルが issue の本文から書いたものです。