Fix wrong hint when deleting a branch successfully from pull request UI (go-gitea#22673) (go-gitea#22698)

Backport go-gitea#22673

Fix go-gitea#18785

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

Author: yardenshoham

routers/web/repo/pull.go

@@ -1381,7 +1381,7 @@ func CleanUpPullRequest(ctx *context.Context) {
 }
 
 func deleteBranch(ctx *context.Context, pr *issues_model.PullRequest, gitRepo *git.Repository) {
-	fullBranchName := pr.HeadRepo.Owner.Name + "/" + pr.HeadBranch
+	fullBranchName := pr.HeadRepo.FullName() + ":" + pr.HeadBranch
 	if err := repo_service.DeleteBranch(ctx.Doer, pr.HeadRepo, gitRepo, pr.HeadBranch); err != nil {
 		switch {
 		case git.IsErrBranchNotExist(err):

tests/integration/pull_merge_test.go

@@ -187,7 +187,7 @@ func TestPullCleanUpAfterMerge(t *testing.T) {
 		htmlDoc := NewHTMLParser(t, resp.Body)
 		resultMsg := htmlDoc.doc.Find(".ui.message>p").Text()
 
-		assert.EqualValues(t, "Branch 'user1/feature/test' has been deleted.", resultMsg)
+		assert.EqualValues(t, "Branch 'user1/repo1:feature/test' has been deleted.", resultMsg)
 	})
 }