Update link to WAI-ARIA combobox example

The previous link is no longer extant (redirects to the landing page for
the authoring guide). The current implementation supports the documented
navigation and behavior guidelines in that example, except where not
applicable (e.g. there is no way to explicitly open the listbox if it is
empty). These types of allowed exceptions are alluded to on
https://www.w3.org/WAI/ARIA/apg/patterns/combobox/

src/sidebar/components/TagEditor.tsx

@@ -24,8 +24,8 @@ export type TagEditorProps = {
 /**
  * Component to edit annotation's tags.
  *
- * Component accessibility is modeled after "Combobox with Listbox Popup Examples" found here:
- * https://www.w3.org/TR/wai-aria-practices/examples/combobox/aria1.1pattern/listbox-combo.html
+ * Component accessibility is modeled after "Combobox with Listbox Autocomplete Example" found here:
+ * https://www.w3.org/WAI/ARIA/apg/example-index/combobox/combobox-autocomplete-list.html
  */
 function TagEditor({
   onAddTag,