ci: use pnpm setup action

Author: Hrdtr

.github/workflows/ci.yml

@@ -13,6 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
       - uses: actions/setup-node@v4
         with:
           node-version: 22