test_upstream_compat: update for pmb v3

Update the testcases to use the new pmb v3 API.

Depends on pmbootstrap!2438 (merged)

Fix #9 (closed)

.ci/flake8.sh

-#!/bin/sh -e
-topdir="$(realpath "$(dirname "$0")/..")"
-cd "$topdir"
-
-flake8 $(find -name '*.py')
-
-echo "flake8 check passed"