treewide: cleanup error string formatting

Change-Id: I9012ba58dded916984468219b214200144a439b9
Reviewed-on: https://review.monogon.dev/c/monogon/+/3023
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Vouch-Run-CI: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/core/metrics/metrics.go b/metropolis/node/core/metrics/metrics.go
index ffae970..bd229fa 100644
--- a/metropolis/node/core/metrics/metrics.go
+++ b/metropolis/node/core/metrics/metrics.go
@@ -140,5 +140,5 @@
 	if err != nil && ctx.Err() != nil {
 		return ctx.Err()
 	}
-	return fmt.Errorf("Serve: %w", err)
+	return fmt.Errorf("Serve(): %w", err)
 }