Drop Python 3.8 support

[ogajduse]

Problem statement

In #471, we have hit issues running wrapanapi unit tests with Python 3.8. Errors related to typing library were showing up.

Solution

Unit tests using Python 3.9 do not throw any error, therefore we can drop Python 3.8.
After talking to @mshriver, we should be good to drop Python 3.8 since all known wrapanapi users are using 3.9+.

[mshriver]

Agree with dropping 3.8 support here even if py3.8 is still supported in general.

Known consumers are on py3.9+ at this point, and we otherwise have enough changes on master to warrant a minor release (including dropping py3.7).