style: format code with Go fmt and Gofumpt

This commit fixes the style issues introduced in e724ddb according to the output
from Go fmt and Gofumpt.

Details: #1

Author: deepsource-autofix[bot]

lura/proxy.go

@@ -39,8 +39,8 @@ var (
 // Middleware creates a proxy that instruments the proxy it wraps by creating an span if enabled,
 // and report the duration of this stage in metrics if enabled.
 func Middleware(staticAttrs []attribute.KeyValue, gsf state.GetterFn, metricsEnabled bool, tracesEnabled bool,
-	spanName string) proxy.Middleware {
-
+	spanName string,
+) proxy.Middleware {
 	if gsf == nil {
 		gsf = state.GlobalState
 	}