patch 9.0.1999: Vim9: some error messages can be improved

Problem:  Vim9: some error messages can be improved
Solution: Mention the defining class for variable access error message

closes: #13272

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Co-authored-by: Ernie Rael <errael@raelity.com>
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 136bea4..828fe02 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -1616,7 +1616,7 @@
 	char *msg = (m->ocm_access == VIM_ACCESS_PRIVATE)
 				? e_cannot_access_private_variable_str
 				: e_variable_is_not_writable_str;
-	semsg(_(msg), m->ocm_name, cl->class_name);
+	emsg_var_cl_define(msg, m->ocm_name, 0, cl);
 	return FALSE;
     }