Why is workbox writing files to tmp/build instead of public on deployment?

[eleventhaus]

If I run my build script locally, workbox writes files to the public directory:

> react-scripts build && workbox generateSW workbox-config.js

Creating an optimized production build...
Compiled successfully.

File sizes after gzip:

  405.84 kB  build/static/js/main.0a2b00bf.js
  2.63 kB    build/static/js/685.d490ac7a.chunk.js
  831 B      build/static/js/91.541a4e54.chunk.js
  811 B      build/static/js/153.7aa0b5d4.chunk.js
  806 B      build/static/js/832.8de07afe.chunk.js
  733 B      build/static/js/844.63deabe8.chunk.js
  728 B      build/static/js/580.d7932d4f.chunk.js

The project was built assuming it is hosted at /.
You can control this with the homepage field in your package.json.

The build folder is ready to be deployed.
You may serve it with a static server:

  npm install -g serve
  serve -s build

Find out more about deployment here:

  https://cra.link/deployment

Using configuration from /root/workbox-config.js.
The service worker files were written to:
  • /root/public/sw.js
  • /root/public/sw.js.map
  • /root/public/workbox-74969ce0.js
  • /root/public/workbox-74969ce0.js.map
The service worker will precache 7 URLs, totaling 177 kB.

But during deployment, workbox writes the files to the tmp directory:

remote:        > react-scripts build && workbox generateSW workbox-config.js
remote:        
remote:        Creating an optimized production build...
remote:        Compiled successfully.
remote:        
remote:        File sizes after gzip:
remote:        
remote:          405.84 kB  build/static/js/main.0a2b00bf.js
remote:          2.63 kB    build/static/js/685.d490ac7a.chunk.js
remote:          831 B      build/static/js/91.541a4e54.chunk.js
remote:          811 B      build/static/js/153.7aa0b5d4.chunk.js
remote:          806 B      build/static/js/832.8de07afe.chunk.js
remote:          733 B      build/static/js/844.63deabe8.chunk.js
remote:          728 B      build/static/js/580.d7932d4f.chunk.js
remote:        
remote:        The project was built assuming it is hosted at /.
remote:        You can control this with the homepage field in your package.json.
remote:        
remote:        The build folder is ready to be deployed.
remote:        You may serve it with a static server:
remote:        
remote:          npm install -g serve
remote:          serve -s build
remote:        
remote:        Find out more about deployment here:
remote:        
remote:          https://cra.link/deployment
remote:        
remote:        Using configuration from /tmp/build_b798eb87/workbox-config.js.
remote:        The service worker files were written to:
remote:          • /tmp/build_b798eb87/public/sw.js
remote:          • /tmp/build_b798eb87/public/sw.js.map
remote:          • /tmp/build_b798eb87/public/workbox-74969ce0.js
remote:          • /tmp/build_b798eb87/public/workbox-74969ce0.js.map
remote:        The service worker will precache 7 URLs, totaling 177 kB.

package.json

{
  ...
  "scripts": {
    "build": "react-scripts build && workbox generateSW workbox-config.js",
  }
  ...
}

workbox-config.js:

module.exports = {
  globDirectory: "public/",
  globPatterns: ["**/*.{png,html,js,ico,json,txt}"],
  swDest: "public/sw.js",
  ignoreURLParametersMatching: [/^utm_/, /^fbclid$/],
  runtimeCaching: [
    {
      urlPattern: /api/,
      handler: "StaleWhileRevalidate",
      options: {
        cacheName: "my-api-cache",
        expiration: {
          maxEntries: 5,
          maxAgeSeconds: 60,
        },
      },
    },
  ],
};

file structure:

root
├── src
├── package.json
└── workbox-config.js

I have tried moving the workbox script to the heroku-cleanup script but that doesn't work. Same thing happens.

How do I get the workbox script to write to the files to the root directory on heroku?