ci: fix deps installation for FreeBSD systems

The issue was in the `deps_freebsd` target that installed test-run deps
(py38-yaml, py38-six, py38-gevent) via the `pkg` package manager.

At some moment these packages were upgraded to 39 version on the mirrors
and became not available for installation anymore.

Now test-run deps are installed via `pip` package installer to avoid
such issues in the future. Installation via `pip` is more robust because
we have deps versions pinned in test-run and also we have python version
pinned to 3.8.

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci