ci: fix missing pnpm

Author: datbth

.github/workflows/test.yaml

@@ -23,4 +23,19 @@ jobs:
       contents: read
     steps:
       - uses: actions/checkout@v4
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+        with:
+          run_install: false
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: 'pnpm'
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
       - run: pnpm validate-links --soft-warnings