Typst writer: omit bibliography if citations not enabled.

With this change, the typst writer will omit the `#bibliography`
command when `citations` is not enabled.  (If you want to use
pandoc's own `--citeproc`, you should combine it with
`-t typst-citations` to disable native typst citations.

Closes #8763.

data/templates/default.typst

@@ -92,6 +92,7 @@ $if(notes)$
 $notes$
 ]
 $endif$
+$if(citations)$
 $if(bibliographystyle)$
 
 #set bibliography(style: "$bibliographystyle$")
@@ -100,6 +101,7 @@ $for(bibliography)$
 
 #bibliography("$bibliography$")
 $endfor$
+$endif$
 $for(include-after)$
 
 $include-after$

src/Text/Pandoc/Writers/Typst.hs

@@ -78,6 +78,9 @@ pandocToTypst options (Pandoc meta blocks) = do
   let context = defField "body" main
               $ defField "notes" notes
               $ defField "toc" (writerTableOfContents options)
+              $ (if isEnabled Ext_citations options
+                    then defField "citations" True
+                    else id)
               $ (case lookupMetaString "lang" meta of
                     "" -> id
                     lang ->