Minimum python in settings.ini incorrect

[synapticarbors]

The minimum python specified in settings.ini is incorrect:
https://github.com/fastai/fastcore/blob/master/settings.ini#L12

When building with python 3.8, you get the following:

File "$PREFIX/lib/python3.8/site-packages/fastcore/py2pyi.py", line 9, in <module>
 │ │ │     from ast import parse, unparse
 │ │ │ ImportError: cannot import name 'unparse' from 'ast' ($PREFIX/lib/python3.8/ast.py)

since unparse was introduced in python 3.9:
https://docs.python.org/3/library/ast.html#ast.unparse