Add $PWD because something changed in the way nuget evaluates cmdline args.

build_native.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 cd $(dirname "$0")
 # Add the local directory as a .NET package source.
-dotnet nuget add source -n ReFuel.StbImage bin
+dotnet nuget add source -n ReFuel.StbImage $PWD/bin
 
 # Build each architecture in its own subfolder.
 DST=$PWD    ./docker-cross-compiler/sh/build_native.sh $PWD linux-arm64