### 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)
int idx = filter->get_selected();
			if (filters.size() > 1) {
				idx--;
			}
			if (idx >= 0 && idx < filters.size()) {
				String flt = filters[idx].get_slice(";", 0);
				int filterSliceCount = flt.get_slice_count(",");
				for (int j = 0; j < filterSliceCount; j++) {
					String str = (flt.get_slice(",", j).strip_edges());
					if (f.match(str)) {
						valid = true;
						break;
					}
				}
				if (!valid && filterSliceCount > 0) {
					String str = (flt.get_slice(",", 0).strip_edges());
					f += str.substr(1, str.length() - 1);
					_request_single_thumbnail(get_current_dir().path_join(f.get_file()));
					file->set_text(f.get_file());
					valid = true;
				}
			} else {
				valid = true;
			}
		}
		
		String file_name = file_text.strip_edges().get_file();
		if (file_name.is_empty()) {
			error_dialog->set_text(TTR("Cannot save file with an empty filename."));
			error_dialog->popup_centered(Size2(250, 80) * EDSCALE);