these 2 derivations will be built:
  /nix/store/5qv8h7c3vshq62ys9i3fm0ihhh2p9vwd-james-haproxy-caddy-proxy-protocol-client.py.drv
  /nix/store/lgqcss62drxsdb3z19z7cb485n26ajbw-james-haproxy-caddy-proxy-protocol-test.drv