Allow symfony/flex in composer.json

Author: alexislefebvre

_build/composer.json

@@ -8,7 +8,10 @@
         "preferred-install": {
             "*": "dist"
         },
-        "sort-packages": true
+        "sort-packages": true,
+        "allow-plugins": {
+            "symfony/flex": true
+        }
     },
     "require": {
         "php": ">=7.4",