Fix NuGet smoke test: remove invalid --source flag

The `dotnet add package --source` flag takes a URI/path, not a
configured source name. Passing "local" was interpreted as a relative
path that doesn't exist, causing "no versions available" errors.
Removing the flag lets dotnet search all configured sources including
the local one added via `dotnet nuget add source`.

Author: CID Agent

.github/workflows/release.yml

@@ -915,7 +915,7 @@ jobs:
           dotnet new console -o smoke
           cd smoke
           dotnet nuget add source "$PWD/../nupkg" -n local
-          dotnet add package Iscc.Lib --source local
+          dotnet add package Iscc.Lib
           cat > Program.cs << 'EOF'
           using Iscc.Lib;
           if (!IsccLib.ConformanceSelftest())
@@ -930,7 +930,7 @@ jobs:
           dotnet new console -o smoke
           cd smoke
           dotnet nuget add source "$PWD\..\nupkg" -n local
-          dotnet add package Iscc.Lib --source local
+          dotnet add package Iscc.Lib
           @"
           using Iscc.Lib;
           if (!IsccLib.ConformanceSelftest())