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)

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3299,
 /**/
     3298,
 /**/