PYTHON-5670 Restore minimal support for Python 3.9

[blink1073]

PYTHON-5670

Changes in this PR

Restores support for PyPy 3.9, PyPy 3.10, and Python 3.9.
Since all of these versions are EoL, we do not test against all scenarios.
Instead we test on latest server with the three standard combinations of topology, auth, and ssl.
We only test on one platform.

Test Plan

Added a "Min Support RHEL8" variant with 9 tasks.

Passing build: https://spruce.mongodb.com/version/6938c98cb2efbb0007254ae8/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is there test coverage?
• Is any followup work tracked in a JIRA ticket? If so, add link(s). N/A

Checklist for Reviewer

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Is all relevant documentation (README or docstring) updated?