patch 9.0.1179: not all errors around inheritance are tested

Problem:    Not all errors around inheritance are tested.
Solution:   Add more tests.  Fix uncovered problems.
diff --git a/src/errors.h b/src/errors.h
index 6fa1abb..de1ae4b 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3438,4 +3438,6 @@
 	INIT(= N_("E1356: \"super\" must be followed by a dot"));
 EXTERN char e_using_super_not_in_class_function[]
 	INIT(= N_("E1357: Using \"super\" not in a class function"));
+EXTERN char e_using_super_not_in_child_class[]
+	INIT(= N_("E1358: Using \"super\" not in a child class"));
 #endif