Publish .snupkg symbols package to NuGet.org (#1345)

The .NET SDK csproj already builds a portable-PDB .snupkg alongside the main .nupkg (IncludeSymbols + SymbolPackageFormat=snupkg, with SourceLink), but the publish workflow only uploaded and pushed the .nupkg, so symbols never reached the NuGet.org symbol server.

Update the publish-dotnet job to include *.snupkg in the uploaded artifact, push the main .nupkg with --no-symbols, then explicitly push the .snupkg to https://api.nuget.org/v3/index.json (which dispatches to NuGet.org's symbol endpoint).

Closes #1213

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

.github/workflows/publish.yml

@@ -129,7 +129,9 @@ jobs:
         uses: actions/upload-artifact@v7.0.0
         with:
           name: dotnet-package
-          path: dotnet/artifacts/*.nupkg
+          path: |
+            dotnet/artifacts/*.nupkg
+            dotnet/artifacts/*.snupkg
       - name: NuGet login (OIDC)
         if: github.ref == 'refs/heads/main'
         uses: NuGet/login@v1
@@ -142,7 +144,9 @@ jobs:
           user: stevesanderson
       - name: Publish to NuGet
         if: github.ref == 'refs/heads/main'
-        run: dotnet nuget push ./artifacts/*.nupkg --api-key ${{ steps.nuget-login.outputs.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate
+        run: |
+          dotnet nuget push ./artifacts/*.nupkg --api-key ${{ steps.nuget-login.outputs.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate --no-symbols
+          dotnet nuget push ./artifacts/*.snupkg --api-key ${{ steps.nuget-login.outputs.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate
 
   publish-rust:
     name: Publish Rust SDK