Upgrade PHPUnit to 13.x

Author: benmatselby

composer.json

@@ -6,7 +6,7 @@
     "guzzlehttp/guzzle": "^7.8"
   },
   "require-dev": {
-    "phpunit/phpunit": "^12",
+    "phpunit/phpunit": "^13.0",
     "phpstan/phpstan": "^2.1",
     "squizlabs/php_codesniffer": "^4.0"
   },