Bump phpunit/phpunit from 13.1.7 to 13.1.8

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 13.1.7 to 13.1.8.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/13.1.8/ChangeLog-13.1.md)
- [Commits](sebastianbergmann/phpunit@13.1.7...13.1.8)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-version: 13.1.8
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]