Experiment with medium machines for CI

[madrob]

Proposed changes

Change the runtime class for CI from large to medium. Most of our builds cap out at 6GB usage so this should be ok. Do not merge until proper analysis has been done of the runtime performance.

Checklist

Put an x in the boxes that apply.

• [x] I have read the CONTRIBUTING document
• [ ] I have run pre-commit run --all-files to format my code / installed pre-commit prior to committing changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have updated the necessary documentation (if needed)

[madrob]

CircleCI build on large machine takes 7 minutes, while a build on medium machine is slightly longer at 9 minutes. However, the medium machine is significantly cheaper, still giving us some good savings on cost.

[awni]

@madrob can we close this or are you still investigating?

[madrob]

Should have been marked ready a while ago. Please merge!