build: specify pnpm version in package.json and ci.yml (#513)

Specify pnpm version in both `package.json` and
`ci.yml` to avoid build errors during deployment.

---------
Closes #512
Co-authored-by: satnaing <satnaingdev@gmail.com>

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
       - name: "📦 Install pnpm"
         uses: pnpm/action-setup@v4
         with:
-          version: 10
+          version: 10.11.1
 
       - name: Use Node.js ${{ matrix.node-version }}
         uses: actions/setup-node@v4

package.json

@@ -2,6 +2,7 @@
   "name": "astro-paper",
   "type": "module",
   "version": "5.2.0",
+  "packageManager": "pnpm@10.11.1",
   "scripts": {
     "dev": "astro dev",
     "build": "astro check && astro build && pagefind --site dist && cp -r dist/pagefind public/",