patch 8.2.3997: Vim9: not enough testing for extend() and map()

Problem:    Vim9: not enough testing for extend() and map().
Solution:   Add more test cases.  Fix uncovered problems.  Remove unused type
            fields.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3997,
 /**/
     3996,
 /**/