Update CI to Node 24

Author: microbit-matt-hillsdon

.github/workflows/build.yml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: '20.x'
+          node-version: '24.x'
           registry-url: 'https://registry.npmjs.org'
           cache: npm
       - uses: microbit-foundation/npm-package-versioner-action@v1