fix(deps): update dependency nodebb-theme-vanilla to v11.2.20 (#8715)

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

install/package.json

@@ -92,7 +92,7 @@
         "nodebb-theme-lavender": "5.0.13",
         "nodebb-theme-persona": "10.2.45",
         "nodebb-theme-slick": "1.2.34",
-        "nodebb-theme-vanilla": "11.2.18",
+        "nodebb-theme-vanilla": "11.2.20",
         "nodebb-widget-essentials": "4.1.2",
         "nodemailer": "^6.4.6",
         "passport": "^0.4.1",