patch 8.2.4250: channel out callback test is flaky on Mac

Problem:    Channel out callback test is flaky on Mac.
Solution:   Assign high priority to the test process. (Ozaki Kiichi,
            closes #9653)
diff --git a/src/version.c b/src/version.c
index 0e95130..0657a15 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4250,
+/**/
     4249,
 /**/
     4248,