fix: fix filter and sorting effect in discussion sidebar (#438)

* fix: fix filter and sorting effect in discussion sidebar

* test: fix test cases

src/discussions/posts/PostsView.jsx

@@ -37,7 +37,7 @@ function CategoryPostsList({ category }) {
   const groupedCategory = useSelector(selectCurrentCategoryGrouping)(category);
   // If grouping at subsection is enabled, only apply it when browsing discussions in context in the learning MFE.
   const topicIds = useSelector(selectTopicsUnderCategory)(enableInContextSidebar ? groupedCategory : category);
-  const posts = useSelector(selectTopicThreads(topicIds));
+  const posts = useSelector(enableInContextSidebar ? selectAllThreads : selectTopicThreads(topicIds));
   return <PostsList posts={posts} topics={topicIds} />;
 }
 

src/discussions/posts/PostsView.test.jsx

@@ -191,7 +191,7 @@ describe('PostsView', () => {
           .toHaveLength(topicThreadCount);
         // When grouping is enabled, topic 1 will be shown, but not otherwise.
         expect(screen.queryAllByText(/this is thread-\d+ in topic some-topic-1/i))
-          .toHaveLength(grouping ? topicThreadCount : 0);
+          .toHaveLength(grouping ? topicThreadCount : 2);
       },
     );
   });