File Cargo.toml of Package failed_wlgreet

```toml
[package]
name = "wlgreet"
version = "0.4.0"
edition = "2018"

[dependencies]
nix = "0.24.0" # Updated from 0.15.0 to 0.24.0
wayland-client = "0.29.4"
wayland-protocols = "0.29.4"
wayland-cursor = "0.29.4"
smithay-client-toolkit = "0.15.4"
serde = "1.0"
serde_json = "1.0"
log = "0.4"
calloop = "0.9.3"
rusttype = "0.8.3"
stb_truetype = "0.3.1"
xcursor = "0.3.4"
```

### Additional Notes
- If the `Cargo.lock` file exists, it should be regenerated after updating the `Cargo.toml` file by running `cargo update`.
- Ensure that the Rust toolchain used for building supports the updated dependencies.

By applying this change, the build process should no longer encounter the unresolved import error related to the `nix` crate.