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

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)
```

routers/web/repo/issue.go

@@ -3503,8 +3503,15 @@ type userSearchResponse struct {
 
 // IssuePosters get posters for current repo's issues/pull requests
 func IssuePosters(ctx *context.Context) {
+	issuePosters(ctx, false)
+}
+
+func PullPosters(ctx *context.Context) {
+	issuePosters(ctx, true)
+}
+
+func issuePosters(ctx *context.Context, isPullList bool) {
 	repo := ctx.Repo.Repository
-	isPullList := ctx.Params(":type") == "pulls"
 	search := strings.TrimSpace(ctx.FormString("q"))
 	posters, err := repo_model.GetIssuePostersWithSearch(ctx, repo, isPullList, search, setting.UI.DefaultShowFullName)
 	if err != nil {

routers/web/web.go

@@ -1151,10 +1151,8 @@ func registerRoutes(m *web.Route) {
 
 	m.Group("/{username}/{reponame}", func() {
 		m.Group("", func() {
-			m.Group("/{type:issues|pulls}", func() {
-				m.Get("", repo.Issues)
-				m.Get("/posters", repo.IssuePosters)
-			})
+			m.Get("/issues/posters", repo.IssuePosters) // it can't use {type:issues|pulls} because other routes like "/pulls/{index}" has higher priority
+			m.Get("/{type:issues|pulls}", repo.Issues)
 			m.Get("/{type:issues|pulls}/{index}", repo.ViewIssue)
 			m.Group("/{type:issues|pulls}/{index}/content-history", func() {
 				m.Get("/overview", repo.GetContentHistoryOverview)
@@ -1276,6 +1274,7 @@ func registerRoutes(m *web.Route) {
 			return cancel
 		})
 
+		m.Get("/pulls/posters", repo.PullPosters)
 		m.Group("/pulls/{index}", func() {
 			m.Get("", repo.SetWhitespaceBehavior, repo.GetPullDiffStats, repo.ViewIssue)
 			m.Get(".diff", repo.DownloadPullDiff)