MAINT: Set NumPy latest supported version to 1.20

[rrjbca]

Description

Set NumPy latest supported version to 1.20. Consistency tests are currently passing using NumPy 1.20.1.

Checklist

• [x] Follow the Contributor Guidelines
• [ ] Write unit tests
• [ ] Write documentation strings
• [ ] Assign someone from your working team to review this pull request
• [x] Assign someone from the infrastructure team to review this pull request