Update to use python 3.9 as a minimum version

Gwcelery is dropping support of python 3.8, so we should update our minimum version for the tests to match.

• Python 3.8 test => python 3.9
• Python 3.9 test => python 3.10

changed milestone to %O4

added O4 label

assigned to @brandon.piotrzkowski

This has been resolved by !116 (merged) by adding tests for python 3.10 and 3.11

closed

mentioned in issue lscsoft/raven#32 (closed)