HBSD: mark BROKEN for devel/elixir-plug
The addition of BROKEN in Makefile is deliberately done below
the version number in order to create a merge conflict
if the port is corrected and updated[1] by the MAINTAINER.
[1] https://github.com/elixir-plug/plug/blob/main/README.md#supported-versions
Signed-off-by: Loic <loic.f@hardenedbsd.org>