Move composer-dependency where it belongs

Author: tvdijen

composer.json

@@ -15,11 +15,11 @@
         "php": "^8.2",
         "ext-mbstring": "*",
 
-        "composer/composer": "~2.8.12",
         "composer-plugin-api": "~2.6.0",
         "simplesamlphp/assert": "~1.9.1"
     },
     "require-dev": {
+        "composer/composer": "~2.8.12",
         "simplesamlphp/simplesamlphp-test-framework": "~1.10.3"
     },
     "config": {