Revert "Also allow PHPUnit version 11."

This reverts commit afff907.

Author: jakzal

composer.json

@@ -11,7 +11,7 @@
     ],
     "require": {
         "php": "~8.1.0 || ~8.2.0 || ~8.3.0",
-        "phpunit/phpunit": "^10.0 || ^11.0"
+        "phpunit/phpunit": "^10.0"
     },
     "autoload": {
         "psr-4": {