Composer: bump the phpunit group with 3 updates

Bumps the phpunit group with 3 updates: [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit), [yoast/phpunit-polyfills](https://github.com/Yoast/PHPUnit-Polyfills) and [wp-phpunit/wp-phpunit](https://github.com/wp-phpunit/wp-phpunit).


Updates `phpunit/phpunit` from 9.6.16 to 9.6.19
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/9.6.19/ChangeLog-9.6.md)
- [Commits](sebastianbergmann/phpunit@9.6.16...9.6.19)

Updates `yoast/phpunit-polyfills` from 1.1.0 to 1.1.1
- [Release notes](https://github.com/Yoast/PHPUnit-Polyfills/releases)
- [Changelog](https://github.com/Yoast/PHPUnit-Polyfills/blob/2.x/CHANGELOG.md)
- [Commits](Yoast/PHPUnit-Polyfills@1.1.0...1.1.1)

Updates `wp-phpunit/wp-phpunit` from 6.4.2 to 6.5.3
- [Commits](wp-phpunit/wp-phpunit@6.4.2...6.5.3)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: phpunit
- dependency-name: yoast/phpunit-polyfills
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: phpunit
- dependency-name: wp-phpunit/wp-phpunit
  dependency-type: direct:development
  update-type: version-update:semver-minor
  dependency-group: phpunit
...

Signed-off-by: dependabot[bot] <support@github.com>