Bump phpunit/phpunit from 9.1.4 to 9.1.5

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 9.1.4 to 9.1.5.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-9.1.md)
- [Commits](sebastianbergmann/phpunit@9.1.4...9.1.5)

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