Can't run dotnet pack with sources/symbols when project uses Paket

Description

I get an error when running dotnet pack with the --include-symbols and --include-source arguments.

\.paket\Paket.Restore.targets(100,5): error : The given path's format is not supported.

Everything works when dropping these arguments.
One strange thing that also happens is that if you build it with the arguments then the build without arguments also fails until you delete the symbols.nuspec file in the obj folder.

Repro steps

Repro:
PaketRepro.zip

1. Extract the repo and go to the root Stuff.Repro
2. Run dotnet pack --include-symbols or dotnet pack --include-source

Expected behavior

The command should output a nuget package for the project and one for the symbols

Actual behavior

Throws error \.paket\Paket.Restore.targets(100,5): error : The given path's format is not supported.

Known workarounds

None

Environment

Paket version: 5.91.0
.Net SDK version: 2.0.0
OS: Windows 10

Reproduce from the linked PaketRepro.zip in the Stuff.Repro root using dotnet pack --include-symbols and --include-source. Inspect .paket/Paket.Restore.targets around line 100 and the generated symbols.nuspec in obj. Done means both packages are produced without the path-format error, and a later pack without those options still works without manually deleting symbols.nuspec.