The image uses mariadb-client instead of mysql-client. This means that anything trying to connect to MySQL 8.0 server will fail by default because the mariaDB client does not include support for the caching_sha2_password plugin. This is a fatal error that can't easily be fixed from outside because MariaDB does not support this authentication mechanism, so in a testing scenario like this, it is not an appropriate substitution. This is how it is configured in CI:

db-seeding:
  stage: build
  services:
    - mysql:8.0

and here's an example of how it fails in a pipeline:

The command "mysql --user="${:LARAVEL_LOAD_USER}" --password="${:LARAVEL_LOAD_PASSWORD}" --host="${:LARAVEL_LOAD_HOST}" --port="${:LARAVEL_LOAD_PORT}" --database="${:LARAVEL_LOAD_DATABASE}" < "${:LARAVEL_LOAD_PATH}"" failed.
Exit Code: 1(General error)
Working directory: /builds/myapp
Output:
================
Error Output:
================
ERROR 1045 (28000): Plugin caching_sha2_password could not be loaded: /usr/lib/x86_64-linux-gnu/mariadb19/plugin/caching_sha2_password.so: cannot open shared object file: No such file or directory

This was fixed once before in a PR, but that was never merged.

A possible workaround would be to manually install the mysql client package prior to running the pipeline, but that should not be something we need to do in a default config.