[MM-64639] Fix styling on thread item header (#31807)

webapp/channels/src/components/threading/global_threads/thread_item/thread_item.scss

@@ -105,7 +105,7 @@
         place-content: center;
     }
 
-    > header {
+    > .thread-item-header {
         position: relative;
         display: grid;
         margin: 0 0 6px;