main/python3: add ctypes patch for python 3.8.1

This PR patches ctypes for Python 3.8.1.
Apparently this issue was introduced while fixing another bug but breaks depending libraries, e.g. ctypesgen (see https://bugs.python.org/msg359834). It was already fixed in Python master (https://github.com/python/cpython/pull/17960), but as Python 3.8.2 is expected in mid feburary, it would be nice to have a running system until then.
The same issue was already filed for Fedora (https://bugzilla.redhat.com/show_bug.cgi?id=1794572).
Build and tested here: https://github.com/mmacata/alpine-python381-patch/releases
Other affected versions (Python 3.7.6 and Python 3.8.0) don't seem to be relevant for alpine, this same patch is also relevant for alpine 3.11.