patch 9.0.1926: Vim9: not enough info in error message

Problem:  Vim9: not enough info in error message
Solution: Add class name, change member to variable, quote names

closes: #13136

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Ernie Rael <errael@raelity.com>
diff --git a/src/eval.c b/src/eval.c
index 93b840e..3f8ce5f 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1570,7 +1570,7 @@
 				if ((flags & GLV_READ_ONLY) == 0)
 				{
 				    semsg(_(e_member_is_not_writable_str),
-					    om->ocm_name);
+					    om->ocm_name, cl->class_name);
 				    return NULL;
 				}
 				break;