main/py3-lxc: add py3-setuptools makedepends to fix build break
Building py3-lxc results in error:
Traceback (most recent call last):
File "setup.py", line 47, in <module>
from setuptools import setup, Extension
ModuleNotFoundError: No module named 'setuptools'
>>> ERROR: py3-lxc: build failed
Adding py3-setuptools to makedepends fixes.