Add pnpm/action-setup to CI workflows

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: silverwind

.github/workflows/ci.yaml

@@ -10,6 +10,7 @@ jobs:
     runs-on: ${{matrix.os}}
     steps:
       - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
       - uses: actions/setup-node@v4
         with:
           node-version: latest