fixes for nightly clippy (#1618)

bridges/relays/utils/src/metrics.rs

@@ -121,7 +121,7 @@ impl From<Option<MetricsAddress>> for MetricsParams {
 /// Returns metric name optionally prefixed with given prefix.
 pub fn metric_name(prefix: Option<&str>, name: &str) -> String {
 	if let Some(prefix) = prefix {
-		format!("{}_{}", prefix, name)
+		format!("{prefix}_{name}")
 	} else {
 		name.into()
 	}