Add a test to show what FIFO does to the dirwalk.

Author: Byron

gix-dir/tests/dir/walk.rs

@@ -18,6 +18,16 @@ use gix_dir::walk::EmissionMode::*;
 use gix_dir::walk::ForDeletionMode;
 use gix_ignore::Kind::*;
 
+#[test]
+#[cfg(unix)]
+fn root_is_fifo() {
+    let root = fixture_in("fifo", "top-level");
+}
+
+#[test]
+#[cfg(unix)]
+fn fifo_in_traversal() {}
+
 #[test]
 fn symlink_to_dir_can_be_excluded() -> crate::Result {
     let root = fixture_in("many-symlinks", "excluded-symlinks-to-dir");