Update to Node 20.11 (Some syntax used in webpack.config needs this minimum version)

Author: harmony7

.github/workflows/test.yml

@@ -12,7 +12,7 @@ jobs:
       - name: Setup Node
         uses: actions/setup-node@v3
         with:
-          node-version: '18'
+          node-version: '20.11'
       - name: Setup Fastly CLI
         uses: fastly/compute-actions/setup@v5
       - name: Install Dependencies