chore: remove Python 3.8 references

[DawoudSheraz]

Achieves part of #1129,

• Update Python 3.8 references to 3.9
• Update Github actions to use 3.9
• Ensure tests are working as expected on 3.9
• compile and upgrade requirements on 3.9 base
• make bundle and make ci-test-bundle are running on 3.9

[regisb]

You will also need to make the following changes:

1. Bump sphinx version in requirements/docs.in
2. Remove some items from nitpick_ignore in docs/conf.py.

[DawoudSheraz]

You will also need to make the following changes:

1. Bump sphinx version in requirements/docs.in
2. Remove some items from nitpick_ignore in docs/conf.py.

I have updated the docs.in the requirements file. As for nitpick_ignore, there were no Python 3.8 specific ignored expressions. I tried removing a few items before Python 3.10 comment but removing them caused the docs to fail locally.

[regisb]

lgtm!

[kdmccormick]

I did not review, but Regis's review should be sufficient. 👍🏻