Disable healthcheck for Synapse workers which serve no web traffic

This was mostly affecting the stream writer (events) worker, which was
being reported as unhealthy. It wasn't causing any issues, but it just
looked odd and was confusing people.

As an alternative to hitting the regular `/health` healthcheck route (on
the "client" API which this stream writer does not expose),
we may have went for hitting some "replication" API endpoint instead.

This is more complicated and likely unnecessary.

roles/custom/matrix-synapse/templates/synapse/systemd/matrix-synapse-worker.service.j2

@@ -23,7 +23,7 @@ ExecStartPre={{ devture_systemd_docker_base_host_command_docker }} create \
 			--read-only \
 			--tmpfs=/tmp:rw,noexec,nosuid,size={{ matrix_synapse_tmp_directory_size_mb }}m \
 			--network={{ matrix_synapse_container_network }} \
-			{% if matrix_synapse_worker_details.port != 0 %}
+			{% if matrix_synapse_worker_details.port != 0 and matrix_synapse_worker_details.webserving %}
 			--health-cmd 'curl -fSs http://localhost:{{ matrix_synapse_worker_details.port }}/health || exit 1' \
 			{% else %}
 			--no-healthcheck \