patch 8.2.3852: Vim9: not enough tests

Problem:    Vim9: not enough tests.
Solution:   Also run existing tests for Vim9 script.  Make errors more
            consistent.
diff --git a/src/errors.h b/src/errors.h
index 3fd8e5a..31f275d 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -286,6 +286,8 @@
 #ifdef FEAT_EVAL
 EXTERN char e_invalid_command_str[]
 	INIT(= N_("E476: Invalid command: %s"));
+EXTERN char e_cannot_index_a_funcref[]
+	INIT(= N_("E695: Cannot index a Funcref"));
 EXTERN char e_list_value_has_more_items_than_targets[]
 	INIT(= N_("E710: List value has more items than targets"));
 EXTERN char e_list_value_does_not_have_enough_items[]