WindowOrWorkerGlobalScope is a mixin

Author: saschanaz

docs/index.bs

@@ -1643,7 +1643,7 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
     <h3 id="self-caches">{{WindowOrWorkerGlobalScope/caches|self.caches}}</h3>
 
     <pre class="idl">
-      partial interface WindowOrWorkerGlobalScope {
+      partial interface mixin WindowOrWorkerGlobalScope {
         [SecureContext, SameObject] readonly attribute CacheStorage caches;
       };
     </pre>