patch 8.1.0817: ":=" command is not tested

Problem:    ":=" command is not tested.
Solution:   Add a test. (Dominique Pelle, closes #3859)
diff --git a/src/version.c b/src/version.c
index 1cd591f..532b449 100644
--- a/src/version.c
+++ b/src/version.c
@@ -788,6 +788,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    817,
+/**/
     816,
 /**/
     815,