patch 8.2.0808: not enough testing for the terminal window

Problem:    Not enough testing for the terminal window.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #6069)  Fix memory
            leak.
diff --git a/src/testdir/test_gui.vim b/src/testdir/test_gui.vim
index 28782f0..c9e3f7f 100644
--- a/src/testdir/test_gui.vim
+++ b/src/testdir/test_gui.vim
@@ -850,8 +850,7 @@
     " assume all the other systems have a cat command
     let cmd = 'cat'
   endif
-  let cmd = ':silent !' . cmd . " test_gui.vim\<CR>\<CR>"
-  call feedkeys(cmd, 'xt')
+  exe "silent !" . cmd . " test_gui.vim"
   " TODO: how to check that the command ran in a separate terminal?
   " Maybe check for $TERM (dumb vs xterm) in the spawned shell?
   let &guioptions = save_guioptions