Fix opening repos when .git is a soft link

[can2049]

Closes #ISSUE

background

If a project is big, some times it will be splited into many small git repos.
google repo is a tool to manage a group of git repos.

But, any small git repo manged by this tool, have a difference with normal git repo.
That is , the path .git in the root of the git repo, is not a normal directory, but a soft link to real git bare dir.

zed can not recognize the git-repo managed git repos

you can use the procedure to genreate this problem

# tested on linux
mkdir -p bad_git_repo_project
cd bad_git_repo_project
git init
echo "hello" > hi.txt
git add .
git commit -m "init commit"
echo "hello world" >> hi.txt

# modify the repo
mv .git ../.real_git_repo
ln -sf ../.real_git_repo .git

with vscode, after opening this project, git works well.
but for Zed, git not work(not git status, no git blame)

how to fix

libgit2 can recognize git repo from the root of the project(dir that have .git).
so, we can recognize the git project by opening from the project root dir, but not the .git dir

This fix also works with normal git project.

before fix

after fix

Release Notes:

• Fixed opening repos when .git is soft link

[can2049]

@cla-bot check

[zed-industries-bot]

	Warnings
⚠️	This PR is missing release notes. Please add a "Release Notes" section that describes the change: Release Notes: - Added/Fixed/Improved ... If your change is not user-facing, you can use "N/A" for the entry: Release Notes: - N/A

Generated by 🚫 dangerJS against 9ca1803

[can2049]

@maxbrunsfeld can you help me review this change?

[cla-bot]

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