Add CI support for Python 3.10

[devstein]

Description

Follow up from https://github.com/jupyter-incubator/sparkmagic/pull/755, this adds Python 3.10 to CI, so we can have a stronger support guarantees.

Checklist

• [x] Wrote a description of my changes above
• [x] Added a bullet point for my changes to the top of the CHANGELOG.md file
• [x] Added or modified unit tests to reflect my changes
• [ ] Manually tested with a notebook
• [ ] If adding a feature, there is an example notebook and/or documentation in the README.md file

[devstein]

Blocked by migrating off nose