update waiting in async tests

Author: Danny McClanahan

tests/markdown-test.el

@@ -3751,7 +3751,8 @@ Detail: https://github.com/jrblevin/markdown-mode/issues/79"
 (defun markdown-test/live-preview-wait ()
   (unless markdown-live-preview-current-buffer-sync-async
     (sit-for (* markdown-live-preview-idle-delay 10))
-    (accept-process-output)))
+    (accept-process-output
+     markdown-live-preview-currently-exporting-process nil nil t)))
 
 (defun markdown-test/live-preview-exports ()
   (markdown-test-temp-file "inline.text"