Update phpstan/phpstan requirement from 2.1.25 to 2.1.28 (#42)

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@2.1.25...2.1.28)

---
updated-dependencies:
- dependency-name: phpstan/phpstan
  dependency-version: 2.1.28
  dependency-type: direct:development
...

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

Author: dependabot[bot]

composer.json

@@ -40,7 +40,7 @@
         "phpspec/prophecy": "^1.18",
         "phpspec/prophecy-phpunit": "^2.0",
         "phpstan/extension-installer": "^1.4",
-        "phpstan/phpstan": "2.1.25",
+        "phpstan/phpstan": "2.1.28",
         "phpstan/phpstan-phpunit": "2.0.7",
         "phpunit/phpunit": "^10 || ^11 || ^12",
         "psalm/plugin-phpunit": "0.19.3",