Update squizlabs/php_codesniffer requirement from ^3.8 to ^3.9

Updates the requirements on [squizlabs/php_codesniffer](https://github.com/PHPCSStandards/PHP_CodeSniffer) to permit the latest version.
- [Release notes](https://github.com/PHPCSStandards/PHP_CodeSniffer/releases)
- [Changelog](https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/master/CHANGELOG.md)
- [Commits](PHPCSStandards/PHP_CodeSniffer@3.8.0...3.9.0)

---
updated-dependencies:
- dependency-name: squizlabs/php_codesniffer
  dependency-type: direct:development
...

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

composer.json

@@ -29,7 +29,7 @@
         "phpspec/prophecy-phpunit": "^2.0",
         "phpstan/phpstan": "^1.10.50",
         "psr/http-factory": "^1.0",
-        "squizlabs/php_codesniffer": "^3.8"
+        "squizlabs/php_codesniffer": "^3.9"
     },
     "autoload": {
         "psr-4": {