Build(deps): Bump symfony/slack-notifier from 6.4.0 to 6.4.2 (#2626)

Bumps [symfony/slack-notifier](https://github.com/symfony/slack-notifier) from 6.4.0 to 6.4.2.
- [Release notes](https://github.com/symfony/slack-notifier/releases)
- [Changelog](https://github.com/symfony/slack-notifier/blob/7.0/CHANGELOG.md)
- [Commits](symfony/slack-notifier@v6.4.0...v6.4.2)

---
updated-dependencies:
- dependency-name: symfony/slack-notifier
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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