patch 8.2.3908: cannot use a script-local function for 'foldtext'

Problem:    Cannot use a script-local function for 'foldtext'.
Solution:   Expand "s:" and "<SID>". (Yegappan Lakshmanan, closes #9411)
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index ba2e259..8a65a89 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -405,6 +405,7 @@
       call assert_equal('[00000あiう]', printf('[%010.7S]', 'あiう'))
 
       call assert_equal('1%', printf('%d%%', 1))
+      call assert_notequal('', printf('%p', "abc"))
   END
   call CheckLegacyAndVim9Success(lines)