Fix pnpm caching

Author: domwebber

.github/workflows/prepare-cache.yml

@@ -23,6 +23,6 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: 20
-          cache: npm
+          cache: pnpm
 
       - run: pnpm ci --prod --prefer-offline --frozen-lockfile

.github/workflows/test.yml

@@ -30,7 +30,7 @@ jobs:
         uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node-version }}
-          cache: npm
+          cache: pnpm
 
       - run: pnpm ci --prefer-offline --no-audit --no-fund
       - run: pnpm run build