chore(ci): Bundle crates under the same version_group

[aborgna-q]

This should solve the diamond problem we had where hugr-core get's a breaking release but hugr-passes only publishes a minor, so cargo automatically updates the latter and we get diverging hugr-core versions on the dependency tree (so the public APIs break).

version_group defines a grouping of versions, where packages that had changes will all be bumped to the same version.
https://release-plz.ieni.dev/docs/config#the-version_group-field

In the previous example, a mayor bump to hugr-core will cause a mayor release for both hugr-passes and hugr.
On the other hand, a change to hugr-passes will not trigger a bump on hugr-core.

An alternative (non-automated) solution to this problem can be done via the semver-trick [0,1], but that's a one-off manual solution more useful to avoid problems for external libraries.

• [0]: https://doc.rust-lang.org/cargo/reference/resolver.html#version-incompatibility-hazards
• [1]: https://github.com/dtolnay/semver-trick

[zrho]

I think that makes sense.