chore: fix PHPUnit version to ^9.3

Author: kenjis

composer.json

@@ -26,6 +26,7 @@
     "codeigniter4/framework": "^4.3"
   },
   "require-dev": {
+    "phpunit/phpunit": "^9.3",
     "psr/container": "2.0.2",
     "codeigniter4/devkit": "^1.0",
     "tatter/patches": "^2.1",