Add test for layout-valign with plain markdown content

Covers the exact scenario from #9109: div syntax with
layout-valign on plain text, no code execution needed.

Author: cderv

tests/docs/smoke-all/2025/11/08/9109-markdown.qmd

@@ -0,0 +1,19 @@
+---
+format:
+  pdf:
+    keep-tex: true
+_quarto:
+  tests:
+    pdf:
+      ensureLatexFileRegexMatches:
+        - ['\\begin\{minipage\}\[t\]']
+        - []
+---
+
+::: {layout="[40, -2, 40]" layout-valign="top"}
+
+Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
+
+Lorem ipsum dolor sit amet, consectetur adipiscing elit
+
+:::