refactor: replace map iteration with maps.Copy/Clone

Signed-off-by: whosehang <whosehang@outlook.com>

testutil/handler.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"maps"
 	"net/http"
 	"net/url"
 	"sort"
@@ -137,9 +138,7 @@ func (app *testHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	app.responseMap[request.String()] = responses[1:]
 
 	responseHeader := w.Header()
-	for k, v := range response.Headers {
-		responseHeader[k] = v
-	}
+	maps.Copy(responseHeader, response.Headers)
 
 	w.WriteHeader(response.StatusCode)