Increase minimal phpunit version to make working tests with PHP 8.1 and lowest deps

Author: andrew-demb

composer.json

@@ -23,7 +23,7 @@
     "doctrine/annotations": "^1.13"
   },
   "require-dev": {
-    "phpunit/phpunit": "^8.4.1",
+    "phpunit/phpunit": "^8.5.28",
     "mouf/picotainer": "^1.1",
     "phpstan/phpstan": "^1.8.2",
     "php-coveralls/php-coveralls": "^2.1.0",