Renamed ctx.User to ctx.Doer. (#19161)

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/topic.go

@@ -15,7 +15,7 @@ import (
 
 // TopicsPost response for creating repository
 func TopicsPost(ctx *context.Context) {
-	if ctx.User == nil {
+	if ctx.Doer == nil {
 		ctx.JSON(http.StatusForbidden, map[string]interface{}{
 			"message": "Only owners could change the topics.",
 		})