Warning in first stage of build pipeline

somewhere between pipelines

• https://codebase.helmholtz.cloud/hifis/overall/hifis.net/-/pipelines/329637

and

• https://codebase.helmholtz.cloud/hifis/overall/hifis.net/-/pipelines/329836

there occured a warning in first stage that remained since then. Needs debugging, I guess.

probably related: long-delayed / non-applied updates of jekyll because also failing pipelines: !833 (closed)