### Godot version

4.1.1

### System information

linux

### Issue description

- When favoriting a path in a `FileDialog`, clicking on it travels to `path/to/dir/`.
- When going up a level from there, it doesn't go to `path/to` but to `path/to/dir` (without the `/`).

[simplescreenrecorder-2023-08-18_09.38.37.webm](https://github.com/godotengine/godot/assets/71937306/00c20ad3-292f-4961-84ed-dbc64906df52)

The problem is either (or both) that:
 - loaded path has a trailing `/`
 - parent dir of `stuff/` is considered to be `stuff`

### Steps to reproduce

favorite a directory and use the feature to navigate to it

### Minimal reproduction project

any (i.e. the project manager's "new project" dialog has one)
list_hb->add_child(item_vb);
	item_vb->set_custom_minimum_size(Size2(320, 0) * EDSCALE);
	HBoxContainer *preview_hb = memnew(HBoxContainer);
	preview_hb->set_v_size_flags(Control::SIZE_EXPAND_FILL);
	item_vb->add_child(preview_hb);
	VBoxContainer *list_vb = memnew(VBoxContainer);
	list_vb->set_h_size_flags(Control::SIZE_EXPAND_FILL);
	l = memnew(Label(TTR("Directories & Files:")));
	l->set_theme_type_variation("HeaderSmall");
	list_vb->add_child(l);
	preview_hb->add_child(list_vb);
	
	item_list = memnew(ItemList);
	item_list->set_v_size_flags(Control::SIZE_EXPAND_FILL);
	item_list->connect("item_clicked", callable_mp(this, &EditorFileDialog::_item_list_item_rmb_clicked));
	item_list->connect("empty_clicked", callable_mp(this, &EditorFileDialog::_item_list_empty_clicked));
	item_list->set_allow_rmb_select(true);
	list_vb->add_child(item_list);
	item_menu = memnew(PopupMenu);
	item_menu->connect("id_pressed", callable_mp(this, &EditorFileDialog::_item_menu_id_pressed));
	add_child(item_menu);
	
	preview_vb = memnew(VBoxContainer);
	preview_hb->add_child(preview_vb);
	CenterContainer *prev_cc = memnew(CenterContainer);
	preview_vb->add_margin_child(TTR("Preview:"), prev_cc);
	preview = memnew(TextureRect);
	prev_cc->add_child(preview);
	preview_vb->hide();
	file_box = memnew(HBoxContainer);