update phpunit

Author: Sean O'Brien

composer.json

@@ -17,7 +17,7 @@
         "illuminate/support": "^5.1 || ^6.0 || ^7.0 || ^8.0 || ^9.0 || ^10.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.0 || ^5.0",
+        "phpunit/phpunit": "^4.0 || ^5.0 || ^9.0",
         "vlucas/phpdotenv": "^1.0 || ^2.0 || ^3.0 || ^4.0 || ^5.0",
         "yoast/phpunit-polyfills": "^1.0"
     },