Avoid run change title process when the title is same (#27467)

If user only changed the target branch or just did nothing and clicked
the `Save` button, you will see the change log as following:

![image](https://github.com/go-gitea/gitea/assets/18380374/d30927dd-9227-4653-8fac-b890ef0b3f88)

This makes no sense, so we should check whether the title is surely
changed before run the `ChangeTitle`.

Author: yp05327

services/issue/issue.go

@@ -53,6 +53,10 @@ func ChangeTitle(ctx context.Context, issue *issues_model.Issue, doer *user_mode
 	oldTitle := issue.Title
 	issue.Title = title
 
+	if oldTitle == title {
+		return nil
+	}
+
 	if err := issues_model.ChangeIssueTitle(ctx, issue, doer, oldTitle); err != nil {
 		return err
 	}