keyword only '*' does not work with documentation

# Example

Hello! Using keyword only argument such as:

```python
#| export

def super_func(
keyword_or_non_keyword_arg, # this is a keyword or non-keyword arg
*,
keyword_only_arg # this is a keyword only arg
) -> str: # return string
"super func"
...

```

makes the documentation not working:

```python
show_doc(super_func)
```

```
super_func
super_func (keyword_or_non_keyword_arg, keyword_only_arg)
super func
| | Type | Details | | – | ——– | ———– | | keyword_or_non_keyword_arg | | this is a keyword or non-keyword arg | | keyword_only_arg | | | | Returns | str | return string |
```

the documentation for keyword_only_arg is absent

# Configuration

Python 3.7.16
nbdev 2.3.12

Start by reproducing the issue with the shown Python 3.7.16 example and show_doc(super_func) in nbdev 2.3.12. Trace how the keyword-only parameter is represented in the generated documentation; done means keyword_only_arg appears with its documentation and the existing parameter details remain correct.

Written by the indexing model from the issue text.