Add new release folder structure (#7667)

_data/sidebars/releases_sidebar.yml

@@ -27,6 +27,8 @@ entries:
       url: /releases/latest/specs.html
   - title: 2024 Releases
     folderitems:
+    - title: June
+      url: /releases/2024-06/index.html
     - title: May
       url: /releases/2024-05/index.html
     - title: April