[0.2] Update PHPUnit to a versions that supports PHP 8.4

On PHPUnit 9.5 there are deprecation errors for PHP8.4. We resolve those by bumping PHPUnit to 9.6. We also made sure our PHPUnit configuration file is up to date to match the new version.

Author: WyriHaximus

composer.json

@@ -20,7 +20,7 @@
         "react/stream": "^1.2"
     },
     "require-dev": {
-        "phpunit/phpunit": "^9.5",
+        "phpunit/phpunit": "^9.6",
         "react/async": "^4 || ^3"
     },
     "autoload": {