Fix download archiver of a commit (#20962)

modules/context/repo.go

@@ -987,6 +987,7 @@ func RepoRefByType(refType RepoRefType, ignoreNotExistErr ...bool) func(*Context
 		}
 
 		ctx.Data["BranchName"] = ctx.Repo.BranchName
+		ctx.Data["RefName"] = ctx.Repo.RefName
 		ctx.Data["BranchNameSubURL"] = ctx.Repo.BranchNameSubURL()
 		ctx.Data["TagName"] = ctx.Repo.TagName
 		ctx.Data["CommitID"] = ctx.Repo.CommitID