Do not try to mount /matrix/ssl when matrix_ssl_retrieval_method is 'none'

Since the switch from `-v` to `--mount` (in 1fca917ad1),
we've regressed when `matrix_ssl_retrieval_method == 'none'`.

In such a case, we don't create `/matrix/ssl` directories at all
and shouldn't be trying to mount them into the `matrix-nginx-proxy`
container.

Previously, with `-v`, Docker would auto-create them, effectively hiding
our mistake. Now that `--mount` doesn't do such auto-creation magic,
the `matrix-nginx-proxy` container was failing to start.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/734

roles/matrix-nginx-proxy/templates/systemd/matrix-nginx-proxy.service.j2

@@ -33,8 +33,10 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-nginx-proxy \
 			--mount type=bind,src={{ matrix_nginx_proxy_base_path }}/nginx.conf,dst=/etc/nginx/nginx.conf,ro \
 			--mount type=bind,src={{ matrix_nginx_proxy_data_path }},dst=/nginx-data,ro \
 			--mount type=bind,src={{ matrix_nginx_proxy_confd_path }},dst=/etc/nginx/conf.d,ro \
+			{% if matrix_ssl_retrieval_method != 'none' %}
 			--mount type=bind,src={{ matrix_ssl_config_dir_path }},dst={{ matrix_ssl_config_dir_path }},ro \
 			--mount type=bind,src={{ matrix_static_files_base_path }},dst={{ matrix_static_files_base_path }},ro \
+			{% endif %}
 			{% for volume in matrix_nginx_proxy_container_additional_volumes %}
 			-v {{ volume.src }}:{{ volume.dst }}:{{ volume.options }} \
 			{% endfor %}