patch 8.2.2511: Vim9: cannot use Vim9 script syntax in some places

Problem:    Vim9: cannot use Vim9 script syntax in some places.
Solution:   Add the :vim9cmd command modifier. Incompatible: Makes ":vim9"
            mean ":vim9cmd" instead of ":vim9script".
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index 6826acf..6ade326 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -709,7 +709,7 @@
   var dir = 'Xruntime/after'
   &rtp ..= ',' .. dir
   mkdir(dir .. '/ftplugin', 'p')
-  writefile(['vim9'], dir .. '/ftplugin/qf.vim')
+  writefile(['vim9script'], dir .. '/ftplugin/qf.vim')
   filetype plugin on
   silent helpgrep grail
   cwindow