Fix metrics listeners for Synapse workers

`::` leads to errors like:

> socket.gaierror: [Errno -9] Address family for hostname not supported

roles/matrix-synapse/templates/synapse/worker.yaml.j2

@@ -32,7 +32,7 @@ worker_listeners:
 {% endif %}
 {% if matrix_synapse_metrics_enabled %}
   - type: metrics
-    bind_addresses: ['::']
+    bind_addresses: ['0.0.0.0']
     port: {{ matrix_synapse_worker_details.metrics_port }}
 {% endif %}
 {% endif %}