Build(deps-dev): Bump rector/rector from 2.3.4 to 2.3.8

Bumps [rector/rector](https://github.com/rectorphp/rector) from 2.3.4 to 2.3.8.
- [Release notes](https://github.com/rectorphp/rector/releases)
- [Commits](rectorphp/rector@2.3.4...2.3.8)

---
updated-dependencies:
- dependency-name: rector/rector
  dependency-version: 2.3.8
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]