Pin voodoo instead of odoc

[tmattio]

The pipeline is currently pining odoc and depends on the main branch of voodoo. However, voodoo has constraints on the version of odoc. We should pin voodoo instead.

[sabine]

As I'm tinkering around with the code and breaking things and seeing more of what the pipeline actually does here... I begin to suspect that the pipeline depends on the main branch of voodoo intentionally - in the sense that we want voodoo updates to propagate to the pipeline automatically, without having to restart the pipeline. 🤔 But this is a thing we should sit down and discuss and clarify together.

It is correct that the pipeline should not pin odoc because that is, conceptually, voodoo's job, though. When voodoo's constraints on odoc change, this should not require an update of the pipeline.

[TheLortex]

Instead of propagating voodoo changes directly in the pipeline, it's also possible to require confirmation from an user in the ocurrent interface.

[sabine]

I think that updating the main branch of voodoo is actually quite reasonable, in terms of confirmation, that we want to update. However, this needs to be documented on voodoo right at the top of the README because it can be quite unexpected for newcomers to voodoo.