composer(deps-dev): bump rector/rector from 0.18.7 to 0.18.8 (#1567)

Bumps [rector/rector](https://github.com/rectorphp/rector) from 0.18.7 to 0.18.8.
- [Release notes](https://github.com/rectorphp/rector/releases)
- [Commits](rectorphp/rector@0.18.7...0.18.8)

---
updated-dependencies:
- dependency-name: rector/rector
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>