[MRG] Don't use deprecated circlci/classic machines

[aaronreidsmith]

Description

circleci/classic machines are being deprecated and removed (blog post). This PR updates our Circle jobs that run on those VMs to run on ubuntu-2004:202111-02 instead

Type of change

• [X] Maintenance change
• [X] CI/CD Change

How Has This Been Tested?

I am hoping CI passes 🤞🏻

Checklist:

• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I have made corresponding changes to the documentation
• [X] My changes generate no new warnings
• [X] I have added tests that prove my fix is effective or that my feature works
• [X] New and existing unit tests pass locally with my changes