Bumped minimum phpunit version to 9.1

Author: PHLAK

composer.json

@@ -29,7 +29,7 @@
     "require-dev": {
         "php": ">=7.4",
         "friendsofphp/php-cs-fixer": "^2.16.1",
-        "phpunit/phpunit": "^9.0",
+        "phpunit/phpunit": "^9.1",
         "psy/psysh": "^0.10",
         "vimeo/psalm": "^3.8"
     },