Details about Problem

Building Nuget.Build.Tasks.Console in source-build results in invalid contentFiles in the generated package. Trailing backslashes in the PackagePath on the two lines linked below cause a double slash in the output package. Related to #7004

https://github.com/NuGet/NuGet.Client/blob/784274cc9b2002ca73055e8134064261118d8a01/src/NuGet.Core/NuGet.Build.Tasks.Console/NuGet.Build.Tasks.Console.csproj#L67-L68

dotnet.exe --version (if appropriate): 5.0.100-preview.4.20258.7
OS version (i.e. win10 v1607 (14393.321)): CentOS Linux 8 (Core)

Worked before? Not sure

Detailed repro steps so we can see the same problem

1. Build Nuget.Build.Tasks.Console on a non-windows OS

2. Inspect the resulting nuspec in Nuget.Build.Tasks.Console.*.nupkg (Note the double slash in contentFiles entries)