tests: use max 10 version

Author: vaiil

composer.json

@@ -23,7 +23,7 @@
     },
     "require-dev": {
         "ext-dom": "*",
-        "phpunit/phpunit": ">=7.0",
+        "phpunit/phpunit": ">=7.0,<10",
         "friendsofphp/php-cs-fixer": "^2.3",
         "escapestudios/symfony2-coding-standard": "^3.0",
         "phpcompatibility/php-compatibility": "^9.0",