Add the minimal mysql/mariadb CLI

Some jobs do need to use the CLI to be able to create
temp databases when running checks. It's only 15M and
the alternative is way, way more complex. That way we
keep everything running within docker.

Dockerfile

@@ -7,7 +7,7 @@ RUN echo "Building for ${TARGETPLATFORM}"
 
 # Install some packages that are useful within the images.
 RUN apt-get update && apt-get install -y \
-    git bc \
+    git bc default-mysql-client-core \
 && rm -rf /var/lib/apt/lists/*
 
 # Install pickle as an easier alternative to PECL, that is not