vim-patch:8.1.0298: window resize test sometimes fails on Mac

Problem:    Window resize test sometimes fails on Mac.
Solution:   Add Test_popup_and_window_resize() to flaky tests.
46fad2ef0b

src/nvim/testdir/runtest.vim

@@ -245,6 +245,7 @@ let s:flaky = [
       \ 'Test_oneshot()',
       \ 'Test_out_cb()',
       \ 'Test_paused()',
+      \ 'Test_popup_and_window_resize()',  " sometimes fails on Mac
       \ 'Test_quoteplus()',
       \ 'Test_quotestar()',
       \ 'Test_reltime()',