ci: Use actions/setup-node.

Author: microbit-carlos

.github/workflows/build.yml

@@ -12,5 +12,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 18
       - run: npm ci
       - run: npm run build