patch 8.2.3856: Vim9: not enough tests

Problem:    Vim9: not enough tests.
Solution:   Run more expression tests also with Vim9. Fix an uncovered
            problem.
diff --git a/src/version.c b/src/version.c
index 873b972..95bcb39 100644
--- a/src/version.c
+++ b/src/version.c
@@ -750,6 +750,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3856,
+/**/
     3855,
 /**/
     3854,