Update phpstan/phpstan requirement from 1.* to 2.* (#4)

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@1.0.0...2.1.17)

---
updated-dependencies:
- dependency-name: phpstan/phpstan
  dependency-version: 2.1.17
  dependency-type: direct:development
...

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

Author: dependabot[bot]

composer.json

@@ -22,7 +22,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "9.*",
-        "phpstan/phpstan": "1.*"
+        "phpstan/phpstan": "2.*"
     },
     "scripts": {
         "test": "./vendor/bin/phpunit",