ci: use npm install instead of npm ci for cross-platform compat

npm ci fails on Linux CI when package-lock.json was generated on macOS,
because platform-specific optional deps (@rollup/rollup-linux-x64-gnu)
are missing from the lockfile. This is a known npm bug (#4828).

.github/workflows/ci.yml

@@ -18,6 +18,6 @@ jobs:
         with:
           node-version: ${{ matrix.node-version }}
           cache: npm
-      - run: npm ci
+      - run: npm install
       - run: npm run lint
       - run: npm test