fix(deps): update dependency nodebb-theme-vanilla to v11.3.9 (#9091)

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

install/package.json

@@ -103,7 +103,7 @@
         "nodebb-theme-lavender": "5.0.16",
         "nodebb-theme-persona": "10.3.9",
         "nodebb-theme-slick": "1.3.6",
-        "nodebb-theme-vanilla": "11.3.8",
+        "nodebb-theme-vanilla": "11.3.9",
         "nodebb-widget-essentials": "5.0.0",
         "nodemailer": "^6.4.6",
         "nprogress": "0.2.0",