add support for PHPUnit 12

Author: Ondřej Ešler

composer.json

@@ -13,7 +13,7 @@
     ],
     "require": {
         "ext-pcntl": "*",
-        "phpunit/phpunit": "^7.0||^8.0||^9.0||^10.0||^11.0"
+        "phpunit/phpunit": "^7.0||^8.0||^9.0||^10.0||^11.0||^12.0"
     },
     "autoload": {
         "psr-4": {