drop python 3.9 support

[bmw]

now that josepy 2.2.0 is out deprecating python 3.9 support, we can do this

the PR that did this for python 3.8 can be seen at #214

[zoracon]

Do we want to slot this for a Josepy release for next month?

[bmw]

good question, but i personally don't think we need to

we released 2.2.0 deprecating support, i think we can just drop support in main, move on in this repo without worrying about python 3.9 support, and do our next release whenever we have something else here we want to ship