Update dependency phpunit/phpunit to v9.5.21

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
phpunit/phpunit (source)	require-dev	patch	9.5.20 -> 9.5.21

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Release Notes

sebastianbergmann/phpunit

### [`v9.5.21`](https://togithub.com/sebastianbergmann/phpunit/compare/9.5.20...9.5.21) [Compare Source](https://togithub.com/sebastianbergmann/phpunit/compare/9.5.20...9.5.21)

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