Let's mimic git.git auto tag fetch behavior.

Related to https://github.com/libgit2/libgit2sharp/pull/927/files#r23450279

git fetch against a newly initialized repository with the following config

[core]
    repositoryformatversion = 0
    filemode = false
    bare = false
    logallrefupdates = true
    symlinks = false
    ignorecase = true
    hideDotFiles = dotGitOnly
[remote "origin"]
    url = https://github.com/libgit2/TestGitRepository
    fetch = +refs/heads/*:refs/remotes/origin/*

outputs

$ git fetch
remote: Counting objects: 68, done.
remote: Total 68 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (68/68), done.
From https://github.com/libgit2/TestGitRepository
 * [new branch]      first-merge -> origin/first-merge
 * [new branch]      master     -> origin/master
 * [new branch]      no-parent  -> origin/no-parent
remote: Counting objects: 1, done.
remote: Total 1 (delta 0), reused 1 (delta 0)
Unpacking objects: 100% (1/1), done.
 * [new tag]         annotated_tag -> annotated_tag
 * [new tag]         blob       -> blob
 * [new tag]         commit_tree -> commit_tree

git is noticing that the server did not automatically send the tags and is performing a second fetch. This second fetch is completely different from the first one

issue にはソースファイルもテストも指定されていません。まず fetch の実装と既存の fetch テストを見つけ、次にサーバーがタグを自動的に送信しない場合の初回 fetch と Git の後続タグ fetch を比較してください。2 回の fetch による実証された動作と一致し、新しく取得されたタグを報告できれば完了です。