chore: update PHPUnit to 9.5

Author: kenjis

composer.json

@@ -21,7 +21,7 @@
     },
     "require-dev": {
         "codeigniter4/framework": "^4.0.4",
-        "phpunit/phpunit": "^8.5"
+        "phpunit/phpunit": "^9.5"
     },
     "autoload": {
         "psr-4": {