With invoke_without_command set commands are not marked as optional

Having

```python
@click.group(invoke_without_command=True)
def main():
    if ctx.invoked_subcommand is not None:
        return
    # do something by default
```

I expect `--help` to output:

```
Usage: app.py [OPTIONS] [COMMAND] [ARGS]...
```

But it outputs:

```
Usage: app.py [OPTIONS] COMMAND [ARGS]...
```

Environment:

- Python version: 3.11.8
- Click version: 8.2.0
