Use Immutable Record for accounts in Redux state (#26559)

app/javascript/mastodon/features/account_timeline/components/header.jsx

@@ -17,7 +17,7 @@ import MovedNote from './moved_note';
 class Header extends ImmutablePureComponent {
 
   static propTypes = {
-    account: ImmutablePropTypes.map,
+    account: ImmutablePropTypes.record,
     onFollow: PropTypes.func.isRequired,
     onBlock: PropTypes.func.isRequired,
     onMention: PropTypes.func.isRequired,