sync: only fetch prob-specs repo once

[ErikSchierboom]

No description provided.

[ee7]

Can we close this PR iin favor of #845? I think I'd prefer just to include it in that one - it's not logically separate, right?

[ErikSchierboom]

it's not logically separate, right?

Well, depends on your viewpoint. But I'm fine with closing it here.

[ee7]

I think it's something that could be a separate commit, I'd just prefer that it not be a separate commit directly on the main branch. Rationale: theoretically, if we wanted to revert the commit that adds the create functionality, maybe we should revert this change too (because it only exists to prepare for the upcoming implementation of create).

If you want to have it as a separate commit in the history on main, I'd argue that it should be a separate commit in a branch for create that's merged via merge commit. But I wouldn't bother.