fix(deps): update dependency nodebb-theme-vanilla to v11.1.21 (#8383)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

install/package.json

@@ -91,7 +91,7 @@
         "nodebb-theme-lavender": "5.0.11",
         "nodebb-theme-persona": "10.1.45",
         "nodebb-theme-slick": "1.2.29",
-        "nodebb-theme-vanilla": "11.1.20",
+        "nodebb-theme-vanilla": "11.1.21",
         "nodebb-widget-essentials": "4.1.0",
         "nodemailer": "^6.4.6",
         "passport": "^0.4.1",