Fix delete pull head ref for DeleteIssue (#20032) (#20034)

Backport #20032 

In DeleteIssue the PR git head reference should be `/refs/pull/xxx/head` not `/refs/pull/xxx`

Fix #19655

Signed-off-by: a1012112796 <1012112796@qq.com>

routers/web/repo/issue.go

@@ -878,6 +878,11 @@ func DeleteIssue(ctx *context.Context) {
 		return
 	}
 
+	if issue.IsPull {
+		ctx.Redirect(fmt.Sprintf("%s/pulls", ctx.Repo.Repository.HTMLURL()), http.StatusSeeOther)
+		return
+	}
+
 	ctx.Redirect(fmt.Sprintf("%s/issues", ctx.Repo.Repository.HTMLURL()), http.StatusSeeOther)
 }
 

services/issue/issue.go

@@ -149,7 +149,7 @@ func DeleteIssue(doer *user_model.User, gitRepo *git.Repository, issue *issues_m
 
 	// delete pull request related git data
 	if issue.IsPull {
-		if err := gitRepo.RemoveReference(fmt.Sprintf("%s%d", git.PullPrefix, issue.PullRequest.Index)); err != nil {
+		if err := gitRepo.RemoveReference(fmt.Sprintf("%s%d/head", git.PullPrefix, issue.PullRequest.Index)); err != nil {
 			return err
 		}
 	}