ci: prepare pnpm before install

Author: PatrickJS

.github/workflows/ci.yml

@@ -22,10 +22,11 @@ jobs:
         uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6
         with:
           node-version: 24
-          cache: pnpm
 
       - name: Enable pnpm
-        run: corepack enable
+        run: |
+          corepack enable
+          corepack prepare pnpm@10.20.0 --activate
 
       - name: Install dependencies
         run: pnpm install --frozen-lockfile