Update libgit2 to 3f8d005

Updating libgit2 to `0a62918`.  The current version in HEAD (`0383fa`) had an unfortunate bug updating the tree cache (https://github.com/libgit2/libgit2/issues/2629) that can cause some issues.
This simple temporary implementation wouldn't be enough to cover the test cases

```
        [Theory]
        [InlineData("git@github.com:org/repo.git", false)]
        [InlineData("git://site.com:80/org/repo.git", true)]
        [InlineData("ssh://user@host.com:80/org/repo.git", false)]
        [InlineData("http://site.com:80/org/repo.git", true)]
        [InlineData("https://github.com:80/org/repo.git", true)]
        [InlineData("ftp://site.com:80/org/repo.git", false)]
        [InlineData("ftps://site.com:80/org/repo.git", false)]
        [InlineData("file:///path/repo.git", true)]
        [InlineData("protocol://blah.meh/whatever.git", false)]
```

...but I think it'd a waste of time to make it more complex for the sake of maintaining an obsolete for *this* function.

I'm :+1: to kill it