Fix MariaDB environment variables (use MARIADB_ prefix)

docker-compose.yml

@@ -45,10 +45,10 @@ services:
     env_file:
       - .env.docker
     environment:
-      MYSQL_DATABASE: ${DB_DATABASE}
-      MYSQL_USER: ${DB_USERNAME}
-      MYSQL_PASSWORD: ${DB_PASSWORD}
-      MYSQL_ROOT_PASSWORD: ${DB_ROOT_PASSWORD}
+      MARIADB_DATABASE: ${DB_DATABASE}
+      MARIADB_USER: ${DB_USERNAME}
+      MARIADB_PASSWORD: ${DB_PASSWORD}
+      MARIADB_ROOT_PASSWORD: ${DB_ROOT_PASSWORD}
     volumes:
       - ./mariadb-11-data:/var/lib/mysql
     networks: