patch 8.2.2739: Vim9: a lambda accepts too many arguments at the script level

Problem:    Vim9: a lambda accepts too many arguments at the script level.
Solution:   Do not set uf_varargs in Vim9 script.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index cb1592a..98f40bb 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -3518,7 +3518,7 @@
       vim9script
       set cpo+=M
       exe 'set rtp^=' .. getcwd() .. '/Xdir'
-      au CmdlineEnter : ++once timer_start(0, () => script#func())
+      au CmdlineEnter : ++once timer_start(0, (_) => script#func())
       setline(1, 'some text')
   END
   call writefile(lines, 'XTest_redraw_cpo')