Include symbol packages (.snupkg) in artifact uploads

Update CI workflow to upload both .nupkg and .snupkg files:
- Artifact upload now includes both package types using multi-line path
- GitHub Packages push uses *.*nupkg pattern to match both extensions

Symbol packages (.snupkg) contain debugging information that helps
developers debug into the library code. Publishing them to GitHub
Packages enables a better debugging experience.

Author: claude

.github/workflows/build.yml

@@ -43,8 +43,10 @@ jobs:
               uses: actions/upload-artifact@v4
               with:
                   name: nuget-packages
-                  path: ./artifacts/*.nupkg
+                  path: |
+                      ./artifacts/*.nupkg
+                      ./artifacts/*.snupkg
 
             - name: Push to GitHub Packages
               if: github.event_name == 'push' && startsWith(github.repository, 'khellang/')
-              run: dotnet nuget push ./artifacts/*.nupkg --source https://nuget.pkg.github.com/${{ github.repository_owner }}/index.json --api-key ${{ secrets.GITHUB_TOKEN }} --skip-duplicate
+              run: dotnet nuget push ./artifacts/*.*nupkg --source https://nuget.pkg.github.com/${{ github.repository_owner }}/index.json --api-key ${{ secrets.GITHUB_TOKEN }} --skip-duplicate