build failed "Source control information is not available - the generated source link is empty"

Hi,

I'm trying to build msbuild (msbuild-16.5.0.12403 and msbuild-16.4.0.56107) in Linux (SL7) with git 2.18.4 and dotNET-Core-SDK/3.1.3 but the build fails with errors like:

```bash
/home/user/.nuget/packages/microsoft.build.tasks.git/1.0.0-beta2-19367-01/build/Microsoft.Build.Tasks.Git.targets(24,5): error : Unable to locate repository with working directory that contains directory '/dev/shm/msbuild/16.5.0/dummy-/msbuild-16.5.0.12403/src/Samples/Dependency'. [/dev/shm/msbuild/16.5.0/dummy-/msbuild-16.5.0.12403/src/Samples/Dependency/Dependency.csproj]
```

I get this same error for several directories.

Could someone give me an explanation on what the error means ? I'm sorry but I don't know what other information I can provide that can be helpful, I don't fully understand what's wrong.

### Steps to reproduce
```bash
wget https://github.com/microsoft/msbuild/archive/v16.4.0.56107.tar.gz
tar -zxvf v16.4.0.56107.tar.gz
cd msbuild-16.4.0.56107
./build.sh
```

### Expected behavior

Build success

### Actual behavior
```bash
/home/x2phasr1/.nuget/packages/microsoft.build.tasks.git/1.0.0-beta2-19367-01/build/Microsoft.Build.Tasks.Git.targets(24,5): error : Unable to locate repository with working directory tha
t contains directory '/dev/shm/msbuild-16.4.0.56107/src/Tasks.UnitTests'. [/dev/shm/msbuild-16.4.0.56107/src/Tasks.UnitTests/Microsoft.Build.Tasks.UnitTests.csproj]
/home/x2phasr1/.nuget/packages/microsoft.sourcelink.common/1.0.0-beta2-19367-01/build/Microsoft.SourceLink.Common.targets(50,5): error : Source control information is not available - the
generated source link is empty. [/dev/shm/msbuild-16.4.0.56107/src/Tasks.UnitTests/Microsoft.Build.Tasks.UnitTests.csproj]
0 Warning(s)
54 Error(s)

Time Elapsed 00:00:59.93
Build failed (exit code '1').
```