patch 8.0.0267: channel test sometimes fails on Mac

Problem:    A channel test sometimes fails on Mac.
Solution:   Add the test to the list of flaky tests.

src/testdir/runtest.vim

@@ -156,6 +156,7 @@ let s:flaky = [
       \ 'Test_reltime()',
       \ 'Test_nb_basic()',
       \ 'Test_communicate()',
+      \ 'Test_close_and_exit_cb()',
       \ 'Test_pipe_through_sort_all()',
       \ 'Test_pipe_through_sort_some()'
       \ ]

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    267,
 /**/
     266,
 /**/