composer: bump phpunit/phpunit from 12.1.4 to 12.3.4

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 12.1.4 to 12.3.4.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/12.3.4/ChangeLog-12.3.md)
- [Commits](sebastianbergmann/phpunit@12.1.4...12.3.4)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-version: 12.3.4
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]