Use bundled npm in node-next frontend tests

Author: cmm-aoi

.github/workflows/frontend.yml

@@ -65,7 +65,6 @@ jobs:
       - uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node_version }}
-      - run: npm install -g npm@6.14.18
       - run: npm install
         working-directory: ./frontend
       - run: npm run test