vim-patch:8.1.2329: mouse multiple click test is a bit flaky

Problem:    Mouse multiple click test is a bit flaky.
Solution:   Add it to the list of flaky tests.
44f0bd878a

src/nvim/testdir/runtest.vim

@@ -297,6 +297,7 @@ let s:flaky_tests = [
       \ 'Test_repeat_three()',
       \ 'Test_state()',
       \ 'Test_stop_all_in_callback()',
+      \ 'Test_term_mouse_multiple_clicks_to_visually_select()',
       \ 'Test_terminal_composing_unicode()',
       \ 'Test_terminal_redir_file()',
       \ 'Test_terminal_tmap()',