Fix Bug "Host key verification failed." for GitLab CI pipeline

Overview

During pip install -r requirements.txt in the CI scripts of our repositories that use "de4l-geodata" as an external library, we get the following error:

Collecting de4l-geodata@ git+ssh://git@git.informatik.uni-leipzig.de/scads/de4l/privacy/de4l-geodata.git@3e4b8bb62db3d39fb4651723e3ee61e8e5c22735
  Cloning ssh://****@git.informatik.uni-leipzig.de/scads/de4l/privacy/de4l-geodata.git (to revision 3e4b8bb62db3d39fb4651723e3ee61e8e5c22735) to /tmp/pip-install-86o3eavj/de4l-geodata_e382f8eebac348689360497217e9570a
  Running command git clone -q 'ssh://****@git.informatik.uni-leipzig.de/scads/de4l/privacy/de4l-geodata.git' /tmp/pip-install-86o3eavj/de4l-geodata_e382f8eebac348689360497217e9570a
  Host key verification failed.
  fatal: Could not read from remote repository.
  Please make sure you have the correct access rights
  and the repository exists.

TODO

• Fix the error by following the affiliated Trello Card.
• Rebase 2-noise2d_definition to this fix.