Update phpstan/phpstan requirement from ^1.10 to ^2.0 (#15)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Markus Staab <[email protected]>
Co-authored-by: Markus Staab <[email protected]>

Author: dependabot[bot]

composer.json

@@ -18,7 +18,7 @@
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^3.43",
-        "phpstan/phpstan": "^1.10",
+        "phpstan/phpstan": "^2.0",
         "phpunit/phpunit": "^9 || ^10.5",
         "redaxo/php-cs-fixer-config": "^1.0"
     },