patch 8.1.0820: test for sending large data over channel sometimes fails

Problem:    Test for sending large data over channel sometimes fails.
Solution:   Handle that the job may have finished early.  Also fix that file
            changed test doesn't work in the GUI and reduce flakyness. (Ozaki
            Kiichi, closes #3861)
diff --git a/src/version.c b/src/version.c
index 3a75c99..e999fd1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -788,6 +788,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    820,
+/**/
     819,
 /**/
     818,