build(deps-dev): update rector/rector requirement

Updates the requirements on [rector/rector](https://github.com/rectorphp/rector) to permit the latest version.
- [Release notes](https://github.com/rectorphp/rector/releases)
- [Commits](rectorphp/rector@0.15.2...0.18.4)

---
updated-dependencies:
- dependency-name: rector/rector
  dependency-type: direct:development
...

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

composer.json

@@ -25,7 +25,7 @@
         "phpstan/phpstan": "^1.9",
         "phpstan/phpstan-phpunit": "^1",
         "phpunit/phpunit": "^9.5",
-        "rector/rector": "^0.15.2",
+        "rector/rector": "^0.18.4",
         "spatie/phpunit-snapshot-assertions": "^4.2",
         "symfony/var-dumper": "^6",
         "thecodingmachine/phpstan-safe-rule": "^1.2"