patch 8.2.3299: Vim9: exists() does not handle much at compile time

Problem:    Vim9: exists() does not handle much at compile time.
Solution:   Handle variable names. (closes #8688)
diff --git a/src/version.c b/src/version.c
index 942f114..6518b3b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3299,
+/**/
     3298,
 /**/
     3297,