[css-shadow-parts-1] fix auto-select for list refs

Author: fergald

css-shadow-parts-1/Overview.bs

@@ -18,7 +18,9 @@ spec:selectors-4;
     type:dfn; text:structural pseudo-class
 spec:dom; type:dfn; for:/; text:shadow root
 spec:infra;
-    type:dfn; text:string
+    type:dfn;
+        text:string
+        text:list
 </pre>
 
 Introduction {#intro}