Bump workbox-webpack-plugin from 6.3.0 to 6.4.1

Bumps [workbox-webpack-plugin](https://github.com/googlechrome/workbox) from 6.3.0 to 6.4.1.
- [Release notes](https://github.com/googlechrome/workbox/releases)
- [Commits](https://github.com/googlechrome/workbox/compare/v6.3.0...v6.4.1

)

---
updated-dependencies:
- dependency-name: workbox-webpack-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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