MM-60241 Ensure RHS post list always fills available space (#28087)

Automatic Merge

webapp/channels/src/components/threading/thread_viewer/thread_viewer.scss

@@ -9,9 +9,16 @@
     }
 
     .post-list__dynamic--RHS {
+        display: flex;
+        height: 100%;
+        flex-direction: column;
         padding-bottom: 8px;
         scrollbar-color: var(--center-channel-color-32) #fff0;
         scrollbar-width: thin;
+
+        & > div[role="list"]:nth-child(1) {
+            margin-top: auto;
+        }
     }
 
     > div {