Bump cssnano from 6.0.2 to 6.0.3 in /backend/servers/explorer-web

Bumps [cssnano](https://github.com/cssnano/cssnano) from 6.0.2 to 6.0.3.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/cssnano@6.0.2...cssnano@6.0.3)

---
updated-dependencies:
- dependency-name: cssnano
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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