chg: test: use --without-python for Debian "sid" builds

Debian "sid" images used in GitLab CI no longer contain the distutils
Python module, which prevents the ./configure script from succeeding on
that operating system.  Instead of explicitly installing optional
dependencies for a branch that is no longer actively maintained, add the
--without-python switch to the ./configure invocations on Debian "sid"
to work around the problem.

Merge branch 'michal/disable-python-for-debian-sid-builds' into 'bind-9.16'

See merge request isc-projects/bind9!9260