patch 8.2.3981: Vim9: debugging a for loop doesn't stop before it starts

Problem:    Vim9: debugging a for loop doesn't stop before it starts.
Solution:   Keep the DEBUG instruction before the expression is evaluated.
            (closes #9456)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3981,
 /**/
     3980,
 /**/