Make default builtin-spack-packages-ref from repos.yaml

[CodeGat]

References ACCESS-NRI/access-spack-packages#353 (comment)

Background

The current default for inputs.builtin-spack-packages-ref is the branch develop. This is consistent with the other inputs.*-ref inputs. However, we are overwriting the currently-set spack-config repos.yaml.

Instead of the default being the bleeding edge of spack/spack-packages, we should default to the ref in the repos.yaml in spack-config at the inputs.spack-config-ref. If there is no value in there either, it should be develop (as is spacks default.

This would mirror the Dockerfile in which spack-config informs the initial versions of the spack packages repositories - if there is no builtin-spack-packages-ref, spack-config informs it.

The PR

• Update default of builtin-spack-packages-ref to repos.yaml, or develop if not set.

Testing

Tested yq locally in the cases for:

• No ref of any kind
• branch/tag/commits in repos.yaml
• Set via builtin-spack-packages-ref

[harshula]

🤞