patch 8.2.1931: Vim9: arguments of extend() not checked at compile time

Problem:    Vim9: arguments of extend() not checked at compile time.
Solution:   Add argument type checking for extend().
diff --git a/src/version.c b/src/version.c
index 93de74d..3385895 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1931,
+/**/
     1930,
 /**/
     1929,