Update default.typst to support csl (#9186)

Typst now supports CSL for its native citation engine, so pandoc
should use a specified `csl` style in the template, falling back to
`bibliographystyle` if `csl` is not specified.

https://typst.app/docs/reference/meta/bibliography/

data/templates/default.typst

@@ -83,7 +83,10 @@ $endif$
 $body$
 
 $if(citations)$
-$if(bibliographystyle)$
+$if(csl)$
+
+#set bibliography(style: "$csl$")
+$elseif(bibliographystyle)$
 
 #set bibliography(style: "$bibliographystyle$")
 $endif$