Support git repositories which use the sparse checkout git feature

Hello!
Git introduced a new feature called sparse-checkout This command is very useful in large repositories containing a lot of projects. Using sparse-checkout and partial repository clone allow substantially reduce occupied by the repository space on local disk.

GitDiffMargin is a useful extension for Visual Studio, This extension uses the libgit2sharp. The extension is not work with repositories uses sparse-checkout because such repositories are not supported.

Reproduction steps

Git Diff Margin get an exception unsupported repository version 1. Only versions up to 0 are supported. while creating a Repository on this line.

Refer to the according GitDiffMargin issue for more info:https://github.com/laurentkempe/GitDiffMargin/issues/356

从第 43 行的 GitDiffMargin/Git/GitCommands.cs 和链接的 GitDiffMargin issue 开始，然后检查 Git 和 libgit2sharp 如何表示 sparse-checkout 仓库。使用一个 sparse-checkout 仓库重现仓库版本异常，并验证打开此类仓库不再失败。