patch 8.2.0469: Vim9: no error for missing ] after list

Problem:    Vim9: no error for missing ] after list.
Solution:   Add error message. Add more tests.
diff --git a/src/userfunc.c b/src/userfunc.c
index 32b9fb5..05e5b7f 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -350,7 +350,10 @@
     e = *arg;
     *arg = skipwhite(*arg);
     if (**arg != '}')
+    {
+	semsg(_("E451: Expected }: %s"), *arg);
 	goto errret;
+    }
     ++*arg;
 
     if (evaluate)