Pin crystal dependencies

[lfoppiano]

The crystal dependency update has been causing problems to this github action, in particular coverallsapp/homebrew-coveralls#71 (comment)

Currently there are Github CI jobs that are failing because of this bug. E.g. https://github.com/grobidOrg/grobid/actions/runs/25102614558/job/73555553240

I recommend you to pin the crystal dependency, i noticed that is not the first tie they cause problems with updates.

[afinetooth]

Thanks @lfoppiano.

We'll look into it.