Update phpstan/phpstan requirement from 1.12.7 to 2.1.1

Updates the requirements on [phpstan/phpstan](https://github.com/phpstan/phpstan) to permit the latest version.
- [Release notes](https://github.com/phpstan/phpstan/releases)
- [Changelog](https://github.com/phpstan/phpstan/blob/2.1.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.12.7...2.1.1)

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

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

composer.json

@@ -30,7 +30,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^9.6.19 || ^10.5.18",
-        "phpstan/phpstan": "1.12.7",
+        "phpstan/phpstan": "2.1.1",
         "friendsofphp/php-cs-fixer": "3.55.0",
         "maglnet/composer-require-checker": "^3.0.0",
         "phpro/grumphp-shim": "^2.0.0"