Install pnpm in ci

Author: nicojs

.github/workflows/ci.yml

@@ -22,6 +22,8 @@ jobs:
         uses: actions/setup-node@v6
         with:
           node-version: ${{ matrix.node-version }}
+      - name: Install pnpm
+        run: npm install -g pnpm
       - name: Install dependencies
         run: npm ci
       - name: Build & lint & test
@@ -35,6 +37,8 @@ jobs:
         uses: actions/setup-node@v6
         with:
           node-version: 'latest'
+      - name: Install pnpm
+        run: npm install -g pnpm
       - name: Install dependencies
         run: npm ci
       - name: test-mutation