Fix capitalization

Co-authored-by: Man from Jupyter <51969207+manfromjupyter@users.noreply.github.com>

packages/toc-extension/src/index.ts

@@ -67,7 +67,7 @@ async function activateTOC(
   toc.title.caption = trans.__('Table of Contents');
   toc.id = 'table-of-contents';
   toc.node.setAttribute('role', 'region');
-  toc.node.setAttribute('aria-label', trans.__('Table of Contents Section'));
+  toc.node.setAttribute('aria-label', trans.__('Table of Contents section'));
 
   labShell.add(toc, 'left', { rank: 400 });