Fix docker building

[JoostBuitink]

Issue addressed

No issue, docker was failing to build on teamcity, due to missing test data (as a result from moving to pixi tasks).

Explanation

Run script to download testdata in the docker file (and remove when done, as these files are not needed inside the docker).

Checklist

• Updated tests or added new tests
• Branch is up to date with master
• Tests & pre-commit hooks pass
• Updated documentation if needed
• Updated changelog.md if needed

Additional Notes (optional)

Add any additional notes or information that may be helpful.

[evetion]

If it works, it works. Note that in the future, you might be able to create a slightly smaller image by combining all Julia steps in one, just like the apt-get step. Every RUN creates it's own layer in the Docker image.