Fix the route for pull-request's authors (#26016) (#26018)

Fix the route for pull-request's authors (#26016) (#26018)

Backport #26016 by @wxiaoguang

Close #25906

![image](https://github.com/go-gitea/gitea/assets/2114189/e689f3e1-9a90-46c0-89f4-2d61394d34d3)

Succeeded logs:

```
[I] router: completed GET /root/test/issues/posters?&q=%20&_=1689853025011 for [::1]:59271, 200 OK in 127.7ms @ repo/issue.go:3505(repo.IssuePosters)

[I] router: completed GET /root/test/pulls/posters?&q=%20&_=1689853968204 for [::1]:59269, 200 OK in 94.3ms @ repo/issue.go:3509(repo.PullPosters)
```

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