chore: move phpunit to require

Fix ComposerRequireChecker error

The following 1 unknown symbols were found:
+----------------------------------------+--------------------+
| Unknown Symbol                         | Guessed Dependency |
+----------------------------------------+--------------------+
| PHPUnit\Framework\MockObject\Stub\Stub |                    |
+----------------------------------------+--------------------+

Author: kenjis

composer.json

@@ -13,10 +13,10 @@
     ],
     "require": {
         "php": "^7.2"
+        "phpunit/phpunit": "^9.5"
     },
     "require-dev": {
-        "bamarni/composer-bin-plugin": "^1.4",
-        "phpunit/phpunit": "^9.5"
+        "bamarni/composer-bin-plugin": "^1.4"
     },
     "autoload": {
         "psr-4": {