patch 8.2.2808: Vim9: increment and decrement not sufficiently tested

Problem:    Vim9: increment and decrement not sufficiently tested.
Solution:   Add assertions.
diff --git a/src/version.c b/src/version.c
index 842a7bc..4b0b1cc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2808,
+/**/
     2807,
 /**/
     2806,