Bug 1758190 - Actually add AccGroupInfo instances to SetAttribute. r=morgan

The browser_obj_group.js test will pass when caching is enabled once
this lands.

Differential Revision: https://phabricator.services.mozilla.com/D140402

accessible/base/AccAttributes.h

@@ -104,6 +104,7 @@ class AccAttributes {
 
   void SetAttribute(nsAtom* aAttrName, AccGroupInfo* aAttrValue) {
     UniquePtr<AccGroupInfo> value(aAttrValue);
+    mData.InsertOrUpdate(aAttrName, AsVariant(std::move(value)));
   }
 
   void SetAttribute(nsAtom* aAttrName, gfx::Matrix4x4&& aAttrValue) {