building ocaml dune projects with salsaci

Currently, when trying to build any OCaml packages using the build system dune, one will receive an error that looks like this:

Error: Too many opam files for package "hello_world":
- debian/output/source_dir/hello_world.opam
- hello_world.opam

To easily test the issue, I created this repository containing a "hello world" project built with dune:

https://salsa.debian.org/josch/dune-hello-world/

To see the error, have a look at the latest CI pipeline results.

What is puzzeling is, where this file debian/output/source_dir/hello_world.opam is coming from. What is it doing there? This duplicate file is what is confusing the dune build system.