[UpdateLibGit2] Add v12 csproj format to description.
Fix indices of test repos so that they're not dirty
Update libgit2 binaries to 99a9c86
Updated API usage.

https://github.com/libgit2/libgit2/compare/06d772d...5d91bea
[Configuration] Use snapshot for Get/Find calls.

Thanks @carlosmn.
[Merge] Keep track of new MergePreference.