Add fs feature to nix dependency (#12702)

# Description
Caught a compilation error using `cargo hack` -- `nu-utils` will not
compile without the `fs` feature enabled for `nix`.

crates/nu-utils/Cargo.toml

@@ -29,4 +29,4 @@ unicase = "2.7.0"
 crossterm_winapi = "0.9"
 
 [target.'cfg(unix)'.dependencies]
-nix = { workspace = true, default-features = false, features = ["user"] }
+nix = { workspace = true, default-features = false, features = ["user", "fs"] }