Update phpstan/phpstan requirement from 2.1.1 to 2.1.5

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@2.1.1...2.1.5)

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

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

composer.json

@@ -29,7 +29,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^9.6.19 || ^10.5.18",
-        "phpstan/phpstan": "2.1.1",
+        "phpstan/phpstan": "2.1.5",
         "friendsofphp/php-cs-fixer": "3.67.0",
         "maglnet/composer-require-checker": "^3.0.0",
         "phpro/grumphp-shim": "^2.0.0"