patch 8.0.1673: terminal window tests are still a bit flaky

Problem:    Terminal window tests are still a bit flaky.
Solution:   Increase the waiting time even more. (Elimar Riesebieter)
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index cd7a2b2..5645625 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -1061,7 +1061,7 @@
 	\ "set t_ts=",
 	\ ], 'Xscript')
   let buf = RunVimInTerminal('-S Xscript', {})
-  call WaitFor({-> bufnr('Xtextfile') > 0}, 2000)
+  call WaitFor({-> bufnr('Xtextfile') > 0}, 5000)
   call assert_equal('Xtextfile', expand('%:t'))
   call assert_true(winnr('$') >= 3)
   return buf