Fix metrics check when disabled

Previously, disabled metrics had no effect and a request to the
`/metrics` route was answered nonetheless.

Remove needles borrow

src/main.rs

@@ -425,6 +425,7 @@ async fn metrics(
     config: &State<Config>,
 ) -> Option<String> {
     if let Some(metrics_config) = &config.metrics {
+        if metrics_config.enabled {
             if let Some(filter) = &metrics_config.ip_filter {
                 if filter.validate(&address.ip()) {
                     return Some(get_metrics(metrics));
@@ -433,6 +434,7 @@ async fn metrics(
                 return Some(get_metrics(metrics));
             }
         }
+    }
 
     warn!("Forbidden request for metrics: {:?}", address);