Move tomlkit dependency to dev group

[yselkowitz]

Description

tomlkit is used only in the packaging tests which are not ordinarily run as part of the normal workflow of a user or downstream packager.

[rwgk]

Looks good to me, but I'm wondering, how did you stumble over this / what problem does this solve? tomlkit is such a light-weight dependency:

$ pip install tomlkit
Collecting tomlkit
  Downloading tomlkit-0.14.0-py3-none-any.whl.metadata (2.8 kB)
Downloading tomlkit-0.14.0-py3-none-any.whl (39 kB)
Installing collected packages: tomlkit
Successfully installed tomlkit-0.14.0

[yselkowitz]

Fedora ELN tracks the dependencies of RHEL packages in preparation for the next RHEL major version, and pybind11 is included in RHEL as a dependency of a couple packages. pybind11 3.0 introduced new build dependencies on scikit-build-core and tomlkit. The former seems unavoidable short of changing the project to a different build backend. While tomlkit would indeed not introduce any additional dependencies, since it is not actually needed here to build and test a package from the source tarball, there is no reason to add it.

[rwgk]

Thanks for the explanation!