Fix git_remote_connect not throwing on non-zero result

Stop testing .NET 5

Fixed calling into native libgit2 on osx-arm64

Remove git protocol from test data

Fix incorrect information in exceptions

Throw NotFoundException if trees are missing when computing diff

Checkout branch looks to remote tracking branches as fallback

Simplify dealing with missing git objects

Set / get supported extensions

Test native libraries using docker for multiple distros

Update LibGit2Sharp.NativeBinaries to 2.0.315-alpha.0.9

Update LibGit2Sharp.NativeBinaries to 2.0.315-alpha.0.7

Change TFM to netcoreapp3.1