Container builder launcher emits a "sh: 0 -c requires an argument" warning

[0xEAB]

The launcher script for the container builder currently emits a warning/error message.
While it does not seem to cause any harm, it doesn’t look quite right.

Connection to <…ip…> port [tcp/ssh] succeeded!
sh: 0: -c requires an argument
Get:1 http://deb.debian.org/debian bookworm InRelease [151 kB]

https://github.com/dlang-dockerized/images/blob/26fa4b42fa7268d18ec41eec710836c19c603cc8/tools/hcloud-build-images.sh

Also: Where does the “Connection […] succeeded” message come from? Do recent versions of netcat emit that?