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.
diff --git a/src/version.c b/src/version.c
index 4d15dbf..170c0c2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3997,
+/**/
     3996,
 /**/
     3995,