[backport] Fix conditionalBlock crash in manuscript

Backport from #13624

Add test to reproduce #13616

Author: cderv

src/resources/filters/layout/manuscript.lua

@@ -57,10 +57,10 @@ function manuscript()
         -- If this is a notebook embed cell, 'lift' the contents of any child divs
         -- up (unroll their contents), this will help us avoid
         -- labeling divs marked as `cells` more than once
-        local blocks = pandoc.List()
+        local blocks = pandoc.Blocks({})
         for _, childBlock in ipairs(divEl.content) do
           if is_regular_node(childBlock, "Div") then
-              tappend(blocks, childBlock.content)
+              blocks:extend(childBlock.content)
           else
             blocks:insert(childBlock)
           end

tests/docs/smoke-all/2025/10/27/13616/.gitignore

@@ -0,0 +1,2 @@
+/.quarto/
+**/*.quarto_ipynb

tests/docs/smoke-all/2025/10/27/13616/13616.qmd

@@ -0,0 +1,13 @@
+---
+title: "Conditional Block in manuscript article"
+_quarto:
+  tests:
+    pdf:
+      noErrors: true
+---
+
+::: {.content-visible when-format="pdf"}
+
+Something
+
+:::

tests/docs/smoke-all/2025/10/27/13616/_quarto.yml

@@ -0,0 +1,9 @@
+project:
+  type: manuscript
+
+manuscript:
+  article: 13616.qmd
+
+format:
+  pdf:
+    pdf-engine: xelatex