ob-screen, use unpredictable temp file name

* lisp/ob-screen.el (org-babel-screen-test): Use unpredictable name
  for temporary file.

lisp/ob-screen.el

@@ -121,7 +121,7 @@ The terminal should shortly flicker."
   (interactive)
   (let* ((session "org-babel-testing")
          (random-string (format "%s" (random 99999)))
-         (tmpfile "/tmp/org-babel-screen.test")
+         (tmpfile (org-babel-temp-file "ob-screen-test-"))
          (body (concat "echo '" random-string "' > " tmpfile "\nexit\n"))
          process tmp-string)
     (org-babel-execute:screen body org-babel-default-header-args:screen)