### 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)
set_process(false);
	preview_waiting = false;
	if (p_preview.is_valid() && get_current_path() == p_path) {
		preview->set_texture(p_preview);
		if (display_mode == DISPLAY_THUMBNAILS) {
			preview_vb->hide();
		} else {
			preview_vb->show();
		}
	} else {
		preview_vb->hide();
		preview->set_texture(Ref<Texture2D>());
	}
}
void EditorFileDialog::_request_single_thumbnail(const String &p_path) {
	if (!FileAccess::exists(p_path) || !previews_enabled) {
		return;
	}
	set_process(true);
	preview_waiting = true;
	preview_wheel_timeout = 0;
	EditorResourcePreview::get_singleton()->queue_resource_preview(p_path, this, "_thumbnail_done", p_path);
}
void EditorFileDialog::_action_pressed() {