ci: standalone compose file for proxy-host-network-mode

This is to prevent the below error with docker-compose v1:

ERROR: for nginx-proxy  "host" network_mode is incompatible with port_bindings

test/test_host-network-mode/test_proxy-host-network-mode.base.yml

@@ -1,5 +1,9 @@
 services:
   nginx-proxy:
+    image: nginxproxy/nginx-proxy:test
+    container_name: nginx-proxy
+    volumes:
+      - /var/run/docker.sock:/tmp/docker.sock:ro
     environment:
       HTTP_PORT: 8888
     network_mode: host