Fix linter
As per doku:
The CLI argument --config is not required. If it is not provided, markdownlint-cli looks for the file .markdownlint.json/.markdownlint.yaml/.markdownlint.yml in current folder, or for the file .markdownlintrc in the current or all parent folders.
And the current folder for preview CI is /src i.e. the root while the config is in a sub folder and hence not found which leads to https://gitlab.hrz.tu-chemnitz.de/zih/hpc-compendium/hpc-compendium/-/merge_requests/136/ failing due to line length >80 instead of >100