fix(ci): remove redundant npm install in sandbox build

Removes the unnecessary `npm install` step from the
`build-and-publish-sandbox` job. The Dockerfile is responsible
for installing the correct version of the package, so this step
was redundant.

.github/workflows/build-and-publish.yml

@@ -92,9 +92,6 @@ jobs:
         with:
           github-token: '${{ secrets.GITHUB_TOKEN }}'
 
-      - name: 'Install Published CLI'
-        run: 'npm install @google/gemini-cli@${{ needs.publish-bundle.outputs.version }}'
-
       - name: 'Log in to GitHub Container Registry'
         uses: 'docker/login-action@v3'
         with: