Fix "init" command when check "mono" dir

What does this MR do and why?

What

修复 mono init 时遇到的 does not look like a git-repo repository 问题

$ mono init -u https://jihulab.com/test-mono/root-group.git -b main
Downloading Repo source from https://jihulab.com/gitlab-cn/mono-client
remote: Enumerating objects: 7947, done.
remote: Counting objects: 100% (110/110), done.
remote: Compressing objects: 100% (51/51), done.
remote: Total 7947 (delta 99), reused 59 (delta 59), pack-reused 7837
接收对象中: 100% (7947/7947), 9.10 MiB | 10.63 MiB/s, 完成.
处理 delta 中: 100% (4190/4190), 完成.
fatal: 'https://jihulab.com/gitlab-cn/mono-client' does not look like a git-repo repository, is --repo-url set correctly?
fatal: double check your --repo-rev setting.
fatal: cloning the git-repo repository failed, will remove '.repo/repo' 

Why

初始化命令执行时，检测了当前仓库仓库中是否有 repo 文件。它应该检查 mono 而不是 repo。

Screenshots or screen recordings

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How to set up and validate locally

按照此步骤安装初始化 mono：https://jihulab.com/gitlab-cn/gitlab/-/issues/3153#note_2612627，会遇到上面提到的报错：https://jihulab.com/gitlab-cn/mono-client/-/merge_requests/5#what 。

手动将 ~/.bin/mono 中的代码应用当前 MR diff 后再执行 init 便不会再报错。

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