Fix an issue with function whitespace causing weirdness

You can see this live here until it's fixed: https://sphinx-notfound-page.readthedocs.io/en/latest/autoapi/notfound/extension/index.html#notfound.extension.html_collect_pages

It outputs RST that looks like this:

```
.. function:: replace_uris(app, doctree, nodetype, nodeattr)
   Replace ``nodetype`` URIs from ``doctree`` to the proper one.

   Rest of the docstring
```

Where we really want the first space there.

autoapi/templates/python/function.rst

@@ -1,6 +1,8 @@
 {% if obj.display %}
 .. function:: {{ obj.short_name }}({{ obj.args }}){% if obj.return_annotation is not none %} -> {{ obj.return_annotation }}{% endif %}
 
+   {# Force Jinja to honor a newline here #}
+   {{''}} 
    {% if obj.docstring %}
    {{ obj.docstring|prepare_docstring|indent(3) }}
    {% endif %}