[css-values-5] Fix issue link

Author: bramus

css-values-5/Overview.bs

@@ -1881,7 +1881,7 @@ Constructing <<custom-ident>> values: the ''ident()'' function</h3>
 	<dfn><<ident-arg>></dfn> = <<string>> | <<integer>> | <<ident>>
 	</pre>
 
-	Issue(w3c/csswg-drafts#11426): Should we allow a fallback value?
+	Issue(w3c/csswg-drafts#11424): Should we allow a fallback value?
 
 	The ''ident()'' function can be used as a value for any property or function argument
 	that accepts a <<custom-ident>>.