Restore PHP 8.1 compatibility

Signed-off-by: Mart Somermaa <mrts@users.noreply.github.com>

Author: mrts

composer.json

@@ -10,7 +10,7 @@
         }
     ],
     "require-dev": {
-        "phpunit/phpunit": "^11.0.4"
+        "phpunit/phpunit": "^10.5"
     },
     "autoload": {
         "psr-4": {
@@ -27,6 +27,7 @@
         }
     },
     "require": {
+        "php": ">=8.1",
         "phpseclib/phpseclib": "3.0.*"
     },
     "scripts": {