Fix error messages and update MysqL client version

[bertrand-lorentz]

Fix handling of missing required env variable.

This also updates the MysQL client version, as the previous version is not available in the repository anymore, causing "docker build" to fail.

[joseluisq]

This also updates the MysQL client version, as the previous version is not available in the repository anymore, causing "docker build" to fail.

No, the previous version still exists.
See https://repo.mysql.com/apt/debian/pool/mysql-8.0/m/mysql-community/mysql-client_8.0.42-1debian12_amd64.deb

Aside from that, can you please create a new PR for the version update just to track it separately?

[bertrand-lorentz]

Thansk for the quick feedback.

I got the following error from "docker build" with the previous version, so I thought I'd handle this in the same PR:

> [ 8/11] RUN set -eux     && DEBIAN_FRONTEND=noninteractive apt-get update -qq     && DEBIAN_FRONTEND=noninteractive apt-get install -qq -y --no-install-recommends         mysql-community-client="8.0.42-1debian12"     && rm -rf /var/lib/apt/lists/*     && rm -rf /var/lib/mysql     && mkdir -p /var/lib/mysql     && chown -R mysql:mysql /var/lib/mysql     && chmod 1777 /var/lib/mysql     && apt-get clean     && rm -rf /var/lib/apt/lists/*     && true:
0.377 + DEBIAN_FRONTEND=noninteractive apt-get update -qq
3.591 + DEBIAN_FRONTEND=noninteractive apt-get install -qq -y --no-install-recommends mysql-community-client=8.0.42-1debian12
4.666 E: Version '8.0.42-1debian12' for 'mysql-community-client' was not found

I'm closing this PR and I'll open 2 new separate PRs, one for each change.