cleanup dev dependencies

composer.json

@@ -37,8 +37,7 @@
     "beberlei/assert": "^3.3"
   },
   "require-dev": {
-    "php": "^7.4",
-    "phpunit/phpunit" : "^9.5",
+    "php": "^8",
     "friendsofphp/php-cs-fixer": "^3.9",
     "phpstan/phpstan": "^1.8",
     "boxblinkracer/phpunuhi": "^1.12"