Lidong Yan [off-list ref] writes：

This patch only adds sorting code to prune_refs(), and as far as I can tell,
prune_refs() is only called once during git fetch. So I was just wondering,
would it be problematic if we moved the string_list_sort() into
refs_warn_dangling_symref() instead? And if it turns out to be safe, could
we perhaps even use strset in refs_warn_dangling_symref()?

Ah, sorry I make a mistake. We can’t sort string_list in refs_warn_dangling_symref().