patch 8.1.0893: terminal test is a bit flaky

Problem:    Terminal test is a bit flaky.
Solution:   Add test_terminal_no_cmd() to list of flaky tests.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 3f49ccb..383e627 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -310,6 +310,7 @@
       \ 'Test_terminal_env()',
       \ 'Test_terminal_hide_buffer()',
       \ 'Test_terminal_make_change()',
+      \ 'Test_terminal_no_cmd()',
       \ 'Test_terminal_noblock()',
       \ 'Test_terminal_redir_file()',
       \ 'Test_terminal_response_to_control_sequence()',