Disable "Composer is slower because of Xdebug" message

Xdebug is indeed enabled, but is set to xdebug.mode=off. This practically disables Xdebug with zero overhead, so this message should be silenced.

compose/docker-compose.yml

@@ -40,6 +40,7 @@ services:
     image: markoshust/magento-php:7.4-fpm-11
     volumes: *appvolumes
     extra_hosts: *appextrahosts
+    env_file: env/phpfpm.env
 
   db:
     image: mariadb:10.4

compose/env/phpfpm.env

@@ -0,0 +1 @@
+COMPOSER_DISABLE_XDEBUG_WARN=1