highlighting quarto document needs the markdown language

Author: cderv

docs/output-formats/html-accessibility.qmd

@@ -69,7 +69,7 @@ As a minimal example of how this works in Quarto, consider this simple document:
 
 ::: light-content
 
-``` qmd
+``` markdown
 ---
 title: Testing Quarto's accessibility checker
 format:
@@ -85,7 +85,7 @@ This violates contrast rules: [insufficient contrast.]{style="color: #eee"}.
 
 ::: dark-content
 
-``` qmd
+``` markdown
 ---
 title: Testing Quarto's accessibility checker
 format: