Microsoft.Build.Tasks.Git: Allow overriding git repositoryformatversion check

Hi,
We just hit an issue over in https://github.com/pythonnet/pythonnet/issues/1613 where a git repository is checked out as part of a build step, but due to interactions between build systems, the `repositoryformatversion` is set to `1`, which then hits the following code in

https://github.com/dotnet/sourcelink/blob/48e002e14a97800c0d6acf24a55357699c9d72a4/src/Microsoft.Build.Tasks.Git/GitDataReader/GitRepository.cs#L120-L125

Which then causes the Python wheel build to fail:

```
C:\Users\WDAGUtilityAccount\.nuget\packages\microsoft.build.tasks.git\1.0.0\build\Microsoft.Build.Tasks.Git.targets(24,5): error : Error reading git repository information: Unsupported repository version 1. Only versions up to 0 are supported. [C:\Users\WDAGUtilityAccount\AppData\Local\Temp\pip-req-build-4vyeo0ym\src\runtime\Python.Runtime.csproj]
C:\Users\WDAGUtilityAccount\.nuget\packages\microsoft.build.tasks.git\1.0.0\build\Microsoft.Build.Tasks.Git.targets(24,5): warning : Unable to locate repository with working directory that contains directory 'C:\Users\WDAGUtilityAccount\AppData\Local\Temp\pip-req-build-4vyeo0ym\src\runtime'. [C:\Users\WDAGUtilityAccount\AppData\Local\Temp\pip-req-build-4vyeo0ym\src\runtime\Python.Runtime.csproj]

Build FAILED.

C:\Users\WDAGUtilityAccount\.nuget\packages\microsoft.build.tasks.git\1.0.0\build\Microsoft.Build.Tasks.Git.targets(24,5): warning : Unable to locate repository with working directory that contains directory 'C:\Users\WDAGUtilityAccount\AppData\Local\Temp\pip-req-build-4vyeo0ym\src\runtime'. [C:\Users\WDAGUtilityAccount\AppData\Local\Temp\pip-req-build-4vyeo0ym\src\runtime\Python.Runtime.csproj]
C:\Users\WDAGUtilityAccount\.nuget\packages\microsoft.build.tasks.git\1.0.0\build\Microsoft.Build.Tasks.Git.targets(24,5): error : Error reading git repository information: Unsupported repository version 1. Only versions up to 0 are supported. [C:\Users\WDAGUtilityAccount\AppData\Local\Temp\pip-req-build-4vyeo0ym\src\runtime\Python.Runtime.csproj]
1 Warning(s)
1 Error(s)
```

Would it be possible to allow overriding this check via a property or environment variable?

I'm not sure what the impact of removing this check completely would be.