specify pnpm version

Author: ueokande

.github/workflows/gh-pages.yml

@@ -17,6 +17,8 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
       - uses: pnpm/action-setup@v3
+        with:
+          version: 9
       - uses: actions/setup-node@v4
         with:
           node-version: 20