ci: bump node version in wpt-theme job (#816)

Author: willdurand

.circleci/config.yml

@@ -57,7 +57,7 @@ jobs:
       - checkout
       - node/install:
           install-yarn: true
-          node-version: "18.18"
+          node-version: "20.18"
       - *restore_build_cache
       - *run_yarn_install
       - *save_build_cache