Fix author list comma behavior

[jchen-cs]

I noticed that the authors list in the publications element did not add commas as expected in some cases.

I believe the issue came from referencing the incorrect variable when iterating through the author list:

hugo-astatine-theme/layouts/partials/publication.html

Line 19 in 17f1644

{{- if le $author_index (len .) -}},{{- end -}}

Since . in this scope refers to author elements, which have a name and optionally me values, it can only have a length of either 1 or 2. Instead, . should be replaced with a reference to the entire list of authors.

The pull request fixes the issue by creating a new variable $authorlist, which may have been what the conditional intended to reference.