Update npm

Update to the latest version of `npm` to ensure trusted publishing is available.

Author: martincostello

.github/workflows/build.yml

@@ -38,6 +38,9 @@ jobs:
         node-version: '22.x'
         registry-url: 'https://registry.npmjs.org'
 
+    - name: Update npm
+      run: npm install -g npm@latest
+
     - name: Install packages
       run: |
         npm ci