Bump phpunit/phpunit from 7.5.12 to 7.5.13

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 7.5.12 to 7.5.13.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-7.5.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/compare/7.5.12...7.5.13

)

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