Add missing makedepends python

Python is required in building, while it is missing in clean chroot:

checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a race-free mkdir -p... /usr/bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking for pkg-config... /usr/bin/pkg-config
checking pkg-config is at least version 0.9.0... yes
checking for udev >= 196... yes
checking for a Python interpreter with version >= 3... none
configure: error: no suitable Python interpreter found

It turns out past versions of base-devel brought python into clean chroot. The package builds successfully using such chroot initially created some time ago, but fails in recently created ones.