Tests for extra images fail

[tarleb]

See https://github.com/pandoc/dockerfiles/actions/runs/15029098845/job/42237066904
Seems like the Eisvogel template cannot be found.

Cc @d@daamien in case you have an idea. Could one of the recent changes have caused this?

[tarleb]

Found the issue, I keep forgetting that env vars are not available at build time if they were defined in a different Dockerfile.

[tarleb]

I realized too late that you were already working on this @daamien. Sorry, I hope I didn't cause any duplicate work.

[daamien]

No problem :)

I found other problems as well so I'm reopening this issue