drop PHPUnit 5

Author: keradus

composer.json

@@ -11,7 +11,7 @@
     ],
     "require": {
         "php": "^7.0 || ^8.0",
-        "phpunit/phpunit": "^5.7.27 || ^6.5.14 || ^7.5.20 || ^8.0 || ^9.0 || ^10.0",
+        "phpunit/phpunit": "^6.5.14 || ^7.5.20 || ^8.0 || ^9.0 || ^10.0",
         "phpunitgoodpractices/polyfill": "^1.4"
     },
     "autoload": {