Fix Clippy warnings

src/header/unistd/mod.rs

@@ -176,7 +176,7 @@ pub unsafe extern "C" fn execvp(file: *const c_char, argv: *const *mut c_char) -
         let path_env = getenv(c_str!("PATH\0").as_ptr());
         if !path_env.is_null() {
             let path_env = CStr::from_ptr(path_env);
-            for mut path in path_env.to_bytes().split(|&b| b == PATH_SEPARATOR) {
+            for path in path_env.to_bytes().split(|&b| b == PATH_SEPARATOR) {
                 let mut program = path.to_vec();
                 program.push(b'/');
                 program.extend_from_slice(file.to_bytes());