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

changed milestone to %ligo-raven 3.1

added suggestion label

assigned to @brandon.piotrzkowski

Similarly to emfollow/ligo-followup-advocate#72 (closed) we should just add a python 3.10 and 3.11 test rather than remove python 3.8.

mentioned in merge request !96 (merged)

closed with merge request !96 (merged)

closed with commit a8df683c