www/bunkerweb: Add missing setuptools run dependency

passlib/pwd.py imports pkg_resources at module level, and that module
lives in setuptools. Nothing in the dependency chain requested it, so
the import only succeeded as long as something else happened to pull
setuptools in. Upstream pins setuptools<81 in the scheduler
requirements for the same reason: pkg_resources is gone in 81.

While here, pin the py-biscuit-auth dependency to ${PY_FLAVOR} now
that the port has flavors.

Sponsored by: Netzkommune GmbH