build-ci: Pin spack-config-ref to fix breaking spack-config change (#653)

# CABLE

Thank you for submitting a pull request to the CABLE Project.

## Description

We are updating our `build-ci` infrastructure so it will be able to
support `spack >= v1.0` more fully. There is an incoming change (see
ACCESS-NRI/spack-config#82) to `spack-config` to
forward this goal, that will no longer work with `build-ci@v2`. There is
a new version of `build-ci@v3` (see
ACCESS-NRI/build-ci#253) that will work with
this new version of `spack-config`, but it is not yet ready for merging.

This interim fix for `build-ci@v2` will work while `build-ci@v3` is
being tested, so there is no downtime between versions, by pinning the
version of `spack-config` to a tag before the breaking change.

> [!NOTE]
> Open pull requests will need to be rebased to get this fix, or a
similar pinning of `spack-config-ref` in the PR added

## Type of change

- [x] Bug fix


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📚 Documentation preview 📚:
https://cable--653.org.readthedocs.build/en/653/

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Author: CodeGat

.github/workflows/ci.yml

@@ -15,6 +15,7 @@ jobs:
     uses: access-nri/build-ci/.github/workflows/ci-github-hosted.yml@v2
     with:
       spack-manifest-path: ${{ matrix.spack-manifest-path }}
+      spack-config-ref: 2025.11.000  # Before build-ci@v2-breaking change to spack-config, don't go any further forward!
       spack-packages-ref: api-v2  # This branch contains the package defs compatible with spack >=1.0. May be incorporated into the main branch
       spack-ref: releases/v1.0
       allow-ssh-into-spack-install: false