patch 8.2.3253: channel test fails randomly

Problem:    Channel test fails randomly.
Solution:   Add a sleep after sending the "echoerr" command. (Michael Soyka)
diff --git a/src/version.c b/src/version.c
index ebd2c56..b01127c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3253,
+/**/
     3252,
 /**/
     3251,