patch 8.2.0278: channel test is flaky on Mac

Problem:    Channel test is flaky on Mac.
Solution:   Reset variable before sending message.
diff --git a/src/version.c b/src/version.c
index b76a354..d74b0fa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    278,
+/**/
     277,
 /**/
     276,