Bump phpunit/phpunit from 9.3.8 to 9.3.9

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 9.3.8 to 9.3.9.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-9.3.md)
- [Commits](sebastianbergmann/phpunit@9.3.8...9.3.9)

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