ci: usage of Node.js v18 (instead of v20) to accommodate mock-fs issue

Ref: tschaub/mock-fs#377, tschaub/mock-fs#380

.github/workflows/test.yml

@@ -15,7 +15,7 @@ jobs:
       - name: "Setup Node.js"
         uses: "actions/setup-node@v4.0.1"
         with:
-          node-version: "lts/*"
+          node-version: "18.x"
           cache: "npm"
 
       - name: "Install dependencies"