Pull request automation: use full npm install (WordPress#66314)

Remove single-package installation from this workflow that creates problems
when migrating to npm workspaces.

The regular npm install workflow is frequently available in cache.

---

Co-authored-by: sirreal <jonsurrell@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>

.github/workflows/pull-request-automation.yml

@@ -17,24 +17,8 @@ jobs:
                   ref: trunk
                   show-progress: ${{ runner.debug == '1' && 'true' || 'false' }}
 
-            - name: Use desired version of Node.js
-              uses: actions/setup-node@0a44ba7841725637a19e28fa30b79a866c81b0a6 # v4.0.4
-              with:
-                  node-version-file: '.nvmrc'
-                  check-latest: true
-
-            - name: Cache NPM packages
-              uses: actions/cache@3624ceb22c1c5a301c8db4169662070a689d9ea8 # v4.1.1
-              with:
-                  # npm cache files are stored in `~/.npm` on Linux/macOS
-                  path: ~/.npm
-                  key: ${{ runner.os }}-node-${{ matrix.node }}-npm-pr-automation-cache-${{ hashFiles('**/package-lock.json') }}
-
-            # Changing into the action's directory and running `npm install` is much
-            # faster than a full project-wide `npm ci`.
-            - name: Install NPM dependencies
-              run: npm install
-              working-directory: packages/project-management-automation
+            - name: Setup Node.js and install dependencies
+              uses: ./.github/setup-node
 
             - uses: ./packages/project-management-automation
               with: