Backport PR #12474: Update copyright date to 2022 in the about dialog (#12475)

Co-authored-by: Jeremy Tuloup <jeremy.tuloup@gmail.com>

packages/help-extension/src/index.tsx

@@ -135,7 +135,7 @@ const about: JupyterFrontEndPlugin<void> = {
         );
         const copyright = (
           <span className="jp-About-copyright">
-            {trans.__('© 2015-2021 Project Jupyter Contributors')}
+            {trans.__('© 2015-2022 Project Jupyter Contributors')}
           </span>
         );
         const body = (