patch 8.2.2063: Vim9: only one level of indexing supported

Problem:    Vim9: only one level of indexing supported.
Solution:   Handle more than one index in an assignment.
diff --git a/src/errors.h b/src/errors.h
index 69450eb..b8ec986 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -311,3 +311,5 @@
 	INIT(= N_("E1139: Missing matching bracket after dict key"));
 EXTERN char e_for_argument_must_be_sequence_of_lists[]
 	INIT(= N_("E1140: For argument must be a sequence of lists"));
+EXTERN char e_indexable_type_required[]
+	INIT(= N_("E1141: Indexable type required"));