Update phpstan/phpstan requirement from ^1.6 to ^1.6 || ^2.0

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/2.0.x/CHANGELOG.md)
- [Commits](phpstan/phpstan@1.6.0...2.0.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

composer.json

@@ -27,7 +27,7 @@
     "require-dev": {
         "phpunit/phpunit": "^9.5",
         "friendsofphp/php-cs-fixer": "^3.8",
-        "phpstan/phpstan": "^1.6",
+        "phpstan/phpstan": "^1.6 || ^2.0",
         "infection/infection": "^0.26.8"
     },
     "scripts": {