Build(deps-dev): Bump rector/rector from 0.12.20 to 0.12.21 (#1998)

Bumps [rector/rector](https://github.com/rectorphp/rector) from 0.12.20 to 0.12.21.
- [Release notes](https://github.com/rectorphp/rector/releases)
- [Commits](rectorphp/rector@0.12.20...0.12.21)

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

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

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