ci: fix npm cache hit condition in pr-preview

Use npm-cache step id so install skips when node_modules restored.

Made-with: Cursor

Author: nicolethoen

.github/workflows/pr-preview.yml

@@ -43,7 +43,7 @@ jobs:
           path: '**/node_modules'
           key: ${{ runner.os }}-npm-14-${{ secrets.CACHE_VERSION }}-${{ hashFiles('package-lock.json') }}
       - run: npm install --frozen-lockfile
-        if: steps.yarn-cache.outputs.cache-hit != 'true'
+        if: steps.npm-cache.outputs.cache-hit != 'true'
       - run: npm run build
         name: Build virtual assistant
       - uses: actions/cache@v4