ci: enable matrix-based Laravel version testing via dynamic Composer require

Replaces static `composer install` with dynamic `composer require`
to match Laravel/Testbench versions based on CI matrix.

Ensures compatibility across Laravel 10–12 and PHP 8.2–8.4.
Improves future-proofing and prevents dependency conflicts.

Author: N3XT0R

composer.json

@@ -17,7 +17,7 @@
     "marcj/topsort": "^1.1"
   },
   "require-dev": {
-    "phpunit/phpunit": "^10.0 || ^11.0",
+    "phpunit/phpunit": "^11.0",
     "orchestra/testbench": "^8.0 || ^9.0 || ^10.0"
   },
   "autoload": {