Bump phpunit/phpunit from 7.2.3 to 7.3.2

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 7.2.3 to 7.3.2.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-6.5.md)
- [Commits](sebastianbergmann/phpunit@7.2.3...7.3.2)

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