add python 3.10 to CI

[mikemhenry]

Description

Provide a brief description of the PR's purpose here.

Todos

• [ ] Implement feature / fix bug
• [ ] Add tests
• [ ] Update documentation as needed
• [ ] Update changelog to summarize changes in behavior, enhancements, and bugfixes implemented in this PR

Status

• [ ] Ready to go

Changelog message

[ijpulidos]

According to https://github.com/choderalab/openmmtools/runs/7661564216?check_suite_focus=true#step:7:3003 we shouldn't import Iterable directly from collections but we should be using collections.abc.Iterable instead (https://docs.python.org/3/library/collections.abc.html#collections.abc.Iterable). This should fix the tests erroring with python 3.10.