python 39 support

[hboisgon]

Issue addressed

Fixes #322
See also: conda-forge/hydromt_wflow-feedstock#21

Explanation

Fix and small release to fix support for python 3.9. Will be dropped again when moving to hydromt v1 / wflow v1

in the end, decided to drop support already to avoid additional testing for python 39

Checklist

• Updated tests or added new tests
• Branch is up to date with main
• Tests & pre-commit hooks pass
• Updated documentation if needed

Additional Notes (optional)

Add any additional notes or information that may be helpful.

[hboisgon]

@savente93 can you help me with the failing py3.9 test? It fails as no cache is found and I have no idea how to fix it.
If this is too much work then we can prematurely drop python 3.9 support but I would like to do a minor release (0.7.1) and I'm not sure what would a number be if python 3.9 is officially dropped?

[savente93]

I'll have a look when I get to work and see if I can fix it. If it's just about a cache in the workflow it should be fairly easy. is this urgent?

[hboisgon]

After some discusssions with @savente93, decided to just drop support for python 39 already as it probably was not working for a while anyhow so no need for a major release.

[hboisgon]

I'm still waiting to see if PR #320 can be part of the release. Once I know, I'll create the release tag. Could you already review @savente93 to see if I added all that is needed to upgrade to python 310? Thanks :)

[savente93]

I think it looks good, although I will say that if you're dopping support for python 3.9 then you can actually keep the X | Y instead of Union[X,Y] and X | None instead of Optional[X] since those syntaxes were added in python 3.10 and I think it looks nicer. At least it doesn't require you to import the Union and Optional types. Though of course it is still valid, so if you preferer it that way you can keep the PR as is. I'll leave that up to you :)