Fix lowest dependency level for phpunit

Author: DEVizzent

composer.json

@@ -25,7 +25,7 @@
     "php": "7.4.*||8.*",
     "guzzlehttp/guzzle": "^7.0",
     "codeception/codeception": "4.*||5.*",
-    "phpunit/phpunit": "8.* || 9.*"
+    "phpunit/phpunit": "^8.5 || 9.*"
   },
   "require-dev": {
     "phpmd/phpmd": "2.*",