ox-md: Fix handling of switches in source blocks

* lisp/ox-md.el (org-md-example-block): handle switches and references
  in source blocks.

lisp/ox-md.el

@@ -157,7 +157,7 @@ channel."
   (replace-regexp-in-string
    "^" "    "
    (org-remove-indentation
-    (org-element-property :value example-block))))
+    (org-export-format-code-default example-block info))))
 
 
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