snakemake test for CI currently disabled

[stolpeo]

Issue

• currently, the Run-Test-Mode github-workflow is disabled (performing CI=true snakemake --cores=1 -p all). this is because data excerpts for the pre-mehari workflow is missing
• the urls in download_urls.yml have to be maintained manually. there might be errors in there as the file is large. it is really hard to maintain (varfish-db-downloader wget urls-download).

Todos

• add all pre-mehari links to download_urls.yml and generate the data excerpts
• make sure all links in download_urls.yml are matching the versions in versions.py and the links used in the rules.
• maybe there is a better strategy? double maintenance is error prone; maintaining the download_urls.yml manually is not trivial.