Carousel: don't set unseen unless it's explicitly `false` (backwards-compat)

app/soapbox/features/feed-filtering/feed-carousel.tsx

@@ -96,7 +96,7 @@ const FeedCarousel = () => {
     if (avatars.length > 0) {
       setSeenAccountIds(
         avatars
-          .filter((avatar) => avatar.seen)
+          .filter((avatar) => avatar.seen !== false)
           .map((avatar) => avatar.account_id),
       );
     }