[PHP]: Update rector/rector requirement from 0.18.3 to 0.18.4

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@0.18.3...0.18.4)

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

Signed-off-by: dependabot[bot] <[email protected]>

composer.json

@@ -36,7 +36,7 @@
         "phpstan/phpstan-doctrine": "1.3.43",
         "phpstan/phpstan-phpunit": "1.3.14",
         "phpstan/phpstan-symfony": "1.3.2",
-        "rector/rector": "0.18.3",
+        "rector/rector": "0.18.4",
         "roave/security-advisories": "dev-master",
         "serendipity_hq/rector-config": "^1.0",
         "symfony/console": "~4.4|~5.4|~6.0",