fix(ci): pin npm to 11.15.0 so npm stage publish works (#10935)

* fix(ci): pin npm to 11.15.0 so npm stage publish works

* docs(ci): note npm pin is temporary until node bundles npm 11.15.0

.github/workflows/publish.yml

@@ -26,6 +26,11 @@ jobs:
           registry-url: 'https://registry.npmjs.org'
           package-manager-cache: false
 
+      # `npm stage publish` requires npm >= 11.15.0, newer than the npm bundled with
+      # this workflow's Node. Remove this step once Node bundles npm >= 11.15.0 by default.
+      - name: Pin npm with staged-publishing support
+        run: npm install -g npm@11.15.0
+
       - name: Install dependencies
         run: npm ci --ignore-scripts