build(deps-dev): Bump mockery/mockery in /phpunit-slicer (#105)

Bumps [mockery/mockery](https://github.com/mockery/mockery) from 1.5.1 to 1.6.6.
- [Release notes](https://github.com/mockery/mockery/releases)
- [Changelog](https://github.com/mockery/mockery/blob/1.6.x/CHANGELOG.md)
- [Commits](mockery/mockery@1.5.1...1.6.6)

---
updated-dependencies:
- dependency-name: mockery/mockery
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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