Update docker-compose.yml

Use a test that fits the 'mysql:9' docker image (instead of a test that uses a 'mariadb' specific entrypoint).

Same fix as in joinloops/loops-server.git

docker-compose.yml

@@ -14,7 +14,7 @@ services:
     volumes:
       - ./mysql-9-data:/var/lib/mysql
     healthcheck:
-      test: ["CMD", "healthcheck.sh", "--connect", "--innodb_initialized"]
+      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "-u", "root", "-p$$MYSQL_ROOT_PASSWORD"]
       interval: 10s
       timeout: 5s
       retries: 3