Merge #1068

1068: simplify buildkite pipeline r=simonbyrne a=simonbyrne

This makes it a bit more explicit about what packages are loaded, and reduces the amount of duplicated info

- [ ] Code follows the [style guidelines](https://clima.github.io/ClimateMachine.jl/latest/DevDocs/CodeStyle/) OR N/A.
- [ ] Unit tests are included OR N/A.
- [ ] Code is exercised in an integration test OR N/A.
- [ ] Documentation has been added/updated OR N/A.


Co-authored-by: Simon Byrne <simonbyrne@gmail.com>

Author: bors[bot]