Updated PHPUnit to 8.4.1

$ composer update phpunit/phpunit --with-all-dependencies

composer.json

@@ -41,7 +41,7 @@
         "doctrine/coding-standard": "^6.0",
         "jetbrains/phpstorm-stubs": "^2019.1",
         "phpstan/phpstan": "^0.11.3",
-        "phpunit/phpunit": "^8.3.3, <8.4.0",
+        "phpunit/phpunit": "^8.4.1",
         "symfony/console": "^2.0.5|^3.0|^4.0|^5.0"
     },
     "suggest": {