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.
diff --git a/src/version.c b/src/version.c
index ba1501c..0b12b2a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    267,
+/**/
     266,
 /**/
     265,