Bump @fortawesome/fontawesome-free from 5.15.2 to 5.15.4 (#551)

Bumps [@fortawesome/fontawesome-free](https://github.com/FortAwesome/Font-Awesome) from 5.15.2 to 5.15.4.
- [Release notes](https://github.com/FortAwesome/Font-Awesome/releases)
- [Changelog](https://github.com/FortAwesome/Font-Awesome/blob/master/CHANGELOG.md)
- [Commits](FortAwesome/Font-Awesome@5.15.2...5.15.4)

---
updated-dependencies:
- dependency-name: "@fortawesome/fontawesome-free"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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